Best Peephole Camera – Reviews and Buyer’s Guide [2020]

by Last Updated July 15, 2020

When it comes to securing your home, every addition to your home security system has a lot of impacts. One such addition is a peephole camera. As the name suggests, it lets you see who is at the door before opening it. A peephole security camera serves multiple purposes- you can use it to see who rang the bell, use it to see the source of any form of a motion at your doorstep, and also use it to deter anyone who may be looking to cause any form of harm. 

Having a peephole camera recorder is one of the basic things that you must do to protect your home, office, or any other property. When you search for a peephole camera, you need to look at what features it offers- such as doorbell ring detection, motion sensing, recording, etc. Further, you also need to check how simple or complex the installation is, wired v/s wireless cameras, the field of view, UI, and much more. Before we get into all that, let’s see what are the best door peephole camera models in the market and what do they offer.

Dmitry Leiko
Author and Today's Expert

Hi there! Dmitry Leiko here, I am the author of the article you've just read, and I write reviews for Expert Bestazy, how you've might guess. I'm passionate about a lot of things, from fishing to reviewing the newest gadgets, I especially adore writing and doing this thorough reviews on absolutely different products, as I've tested a lot of them myself and every time doing long research and advising with experts in a particular field to find the best of the best, I hope you'll find good use of these reviews! :)

Dmitry Leiko
Preview
Best Value for Money
Ring Video Doorbell (1st Gen) – 720p HD video, motion activated alerts, easy installation – Satin Nickel
Best Battery Life
Blink XT2 Outdoor/Indoor Smart Security Camera with cloud storage included, 2-way audio, 2-year battery life – Add-on camera for existing Blink customers
Budget Peephole Camera
digitharbor Video Door Scope Viewer digital peephole viewer door camera outdoor Security Cam Door Open Chime 3 inches Color TFT LCD Screen 120 degrees Wide View Angle with 8G Micro SD memory Card
Highest Video Quality
Ring Video Doorbell 2 with HD Video, Motion Activated Alerts, Easy Installation
Editor’s Choice: Best Security Solution
eufy Security, Wi-Fi Video Doorbell, 2K Resolution, No Monthly Fees, Secure Local Storage,Human Detection, 2-Way Audio, Free Wireless Chime-Requires Existing Doorbell Wires
Best Night Vision Camera
Arlo Video Doorbell | HD Video Quality, 2-Way Audio, Package Detection | Motion Detection and Alerts | Built-in Siren | Night Vision | Easy Installation (Existing Doorbell Wiring Required) | (AVD1001)
Name
Ring Video Doorbell (1st Gen) – 720p HD video, motion activated alerts, easy installation – Satin Nickel
Blink XT2 Outdoor/Indoor Smart Security Camera with cloud storage included, 2-way audio, 2-year battery life – Add-on camera for existing Blink customers
digitharbor Video Door Scope Viewer digital peephole viewer door camera outdoor Security Cam Door Open Chime 3 inches Color TFT LCD Screen 120 degrees Wide View Angle with 8G Micro SD memory Card
Ring Video Doorbell 2 with HD Video, Motion Activated Alerts, Easy Installation
eufy Security, Wi-Fi Video Doorbell, 2K Resolution, No Monthly Fees, Secure Local Storage,Human Detection, 2-Way Audio, Free Wireless Chime-Requires Existing Doorbell Wires
Arlo Video Doorbell | HD Video Quality, 2-Way Audio, Package Detection | Motion Detection and Alerts | Built-in Siren | Night Vision | Easy Installation (Existing Doorbell Wiring Required) | (AVD1001)
Video
720p HD Video, Live View, Night Vision
1080p HD video during the day and with infrared HD night vision after dark
300p Camera Night Vision Wide Angle+Video Record+Photo Shooting
1080p HD Video, Live View, Night Vision
A Crystal-Clear 2K Image: High Definition 2560 x 1920 resolution
Video Doorbell Camera in full HD with HDR
Audio
Two-way talk with noise cancellation
Speaker output and 2-way audio recording
Two-Way Audio
Two-way talk with noise cancellation
2-way audio
2-way audio
Our score
3.5
3.4
3.0
3.6
3.7
3.8
Best Value for Money
Preview
Ring Video Doorbell (1st Gen) – 720p HD video, motion activated alerts, easy installation – Satin Nickel
Name
Ring Video Doorbell (1st Gen) – 720p HD video, motion activated alerts, easy installation – Satin Nickel
Video
720p HD Video, Live View, Night Vision
Audio
Two-way talk with noise cancellation
Our score
3.5
Details
Best Battery Life
Preview
Blink XT2 Outdoor/Indoor Smart Security Camera with cloud storage included, 2-way audio, 2-year battery life – Add-on camera for existing Blink customers
Name
Blink XT2 Outdoor/Indoor Smart Security Camera with cloud storage included, 2-way audio, 2-year battery life – Add-on camera for existing Blink customers
Video
1080p HD video during the day and with infrared HD night vision after dark
Audio
Speaker output and 2-way audio recording
Our score
3.4
Details
Budget Peephole Camera
Preview
digitharbor Video Door Scope Viewer digital peephole viewer door camera outdoor Security Cam Door Open Chime 3 inches Color TFT LCD Screen 120 degrees Wide View Angle with 8G Micro SD memory Card
Name
digitharbor Video Door Scope Viewer digital peephole viewer door camera outdoor Security Cam Door Open Chime 3 inches Color TFT LCD Screen 120 degrees Wide View Angle with 8G Micro SD memory Card
Video
300p Camera Night Vision Wide Angle+Video Record+Photo Shooting
Audio
Two-Way Audio
Our score
3.0
Details
Highest Video Quality
Preview
Ring Video Doorbell 2 with HD Video, Motion Activated Alerts, Easy Installation
Name
Ring Video Doorbell 2 with HD Video, Motion Activated Alerts, Easy Installation
Video
1080p HD Video, Live View, Night Vision
Audio
Two-way talk with noise cancellation
Our score
3.6
Details
Editor’s Choice: Best Security Solution
Preview
eufy Security, Wi-Fi Video Doorbell, 2K Resolution, No Monthly Fees, Secure Local Storage,Human Detection, 2-Way Audio, Free Wireless Chime-Requires Existing Doorbell Wires
Name
eufy Security, Wi-Fi Video Doorbell, 2K Resolution, No Monthly Fees, Secure Local Storage,Human Detection, 2-Way Audio, Free Wireless Chime-Requires Existing Doorbell Wires
Video
A Crystal-Clear 2K Image: High Definition 2560 x 1920 resolution
Audio
2-way audio
Our score
3.7
Details
Best Night Vision Camera
Preview
Arlo Video Doorbell | HD Video Quality, 2-Way Audio, Package Detection | Motion Detection and Alerts | Built-in Siren | Night Vision | Easy Installation (Existing Doorbell Wiring Required) | (AVD1001)
Name
Arlo Video Doorbell | HD Video Quality, 2-Way Audio, Package Detection | Motion Detection and Alerts | Built-in Siren | Night Vision | Easy Installation (Existing Doorbell Wiring Required) | (AVD1001)
Video
Video Doorbell Camera in full HD with HDR
Audio
2-way audio
Our score
3.8
Details

1. Ring Video Doorbell with HD Video – Detailed Review

Sale
Ring Video Doorbell (1st Gen) – 720p HD video, motion activated alerts, easy installation – Satin Nickel
  • 720p HD video doorbell that lets you see, hear and speak to people from your phone, tablet, or select Echo device.
  • Get notifications whenever motion is detected by adjusting your motion zones.
  • With Live View, you can check in on your home any time through the Ring app.
  • Easily setup your Ring Video Doorbell by connecting to wifi via the Ring app and mounting in your desired location.
  • Powered by a built-in rechargeable battery or connects to existing doorbell wiring. With a Ring Protect Plan (subscription sold separately), record all your videos, review what you missed for up to 60 days, and share videos and photos.

The Ring Video Doorbell is a 720p HD video peephole camera. You can see as well as talk to people in front of this camera by connecting through any smartphone, Echo device, or tablet. The motion-sensing feature delivers alerts to the phone which is a handy feature to have. The Live View allows for checking the real-time view from the camera at any time. The rechargeable battery of this can be connected to any doorbell wiring for charging, which is a major convenience factor.

This camera is easy to set up and use even for those who are not very tech-savvy. All required tools and parts for its installation are included in the box. The Android application for this camera can do with several improvements. However, overall, the user-dashboard or control center has the controls to add client devices, select accounts that are linked, and do much more to control privacy and security, making it easy to manage and control.

Pros and Cons

  • Can be connected to any mobile, tablet or Amazon Echo device
  • Simple installation or setup
  • Up to 60-day recording available
  • 720p HD video recording
  • Video recording and photo captures have separate monthly charges
  • Android application is not stable and user-friendly 

2. Blink XT2 Outdoor/Indoor Smart Security Camera – Detailed Review

Sale
Blink XT2 Outdoor/Indoor Smart Security Camera with cloud storage included, 2-way audio, 2-year battery life – Add-on camera for existing Blink customers
  • Extended battery life – 2 year battery life on two AA lithium batteries with a combination of two-way talk, live view, and motion recording. Double the usage of the XT on a single set of batteries when recording video.
  • 2-way audio – Talk to visitors through the Blink app on your smartphone or tablet.
  • Customizable motion detection – Use activity zones to choose where motion is detected so you receive the alerts that matter.
  • Free cloud storage – Keep hundreds of clips stored up to a year with no monthly fees or service contract required.
  • Works with Alexa – View live streams, motion clips, arm and disarm your system, and set up smart reorders for batteries through select Alexa-enabled devices.

Blink’s XT2 peephole door camera not only offers you a range of features but also comes with one of the most active support teams. The company has been quick to update the software on its cameras to resolve many issues which makes it a reliable product overall. This peephole IP camera gets a 2-year battery life powered by 2-AA batteries. You can use their application on your tablet or smartphone for talking to visitors.

While the motion detection feature could use some improvement, it offers decent functionalities and you can set up specific activity zones. It also has night recordings by using Infrared HD. This is easy to set up as there is no wiring required. You also do not need any tools, and it can be used both indoors and outdoors. Unlike other providers that charge you for storage, Blink also bundles this camera with free cloud storage for 1 year without any fees or contracts.

Pros and Cons

  • 2-year battery life
  • Free cloud storage for 1 year 
  • 1080p day recording and infrared night recording
  • Simple set up and installation
  • Motion detection with customizations
  • Limited length of recording for motion detection
  • Connectivity range for WiFi needs improvement 

3. Digitharbor 3.5 inches TFT LCD Screen Digital Door Peephole – Detailed Review

The camera peephole from Digitharbor is a budget pick for those who want something to check their door and nothing more. This is easy to set up a camera that will fit into any door with a barrel thickness between 42 to 70mm. The image sensor produces decent images and you get a 150-degree view through this camera. There are no motion detection or Wi-Fi capabilities. You can use it to view who is at your door at a particular time

It records only when someone rings the bell or when you manually press the record button.  Since there is no Wi-Fi capability, you must use the SD card to view any recordings. Screws and metal brackets for installation are included in the bundle. If you are looking for a device to simply record when the bell rings or view who is at the door, this peephole camera for door does just that within a small budget.

Pros and Cons

  • 3.5” LCD for viewing included
  • Night vision recordings
  • MicroSD card for recording included
  • Decent battery life
  • No Wifi connectivity
  • Lacks motion detection

4. Ring Video Doorbell 2 with HD Video – Detailed Review

Sale
Ring Video Doorbell 2 with HD Video, Motion Activated Alerts, Easy Installation
  • 1080p HD video doorbell that lets you see, hear and speak to people from your phone, tablet, or select Echo device. Includes privacy features, such as customizable privacy zones and audio privacy, to focus only on what's relevant to you.
  • Get notifications whenever motion is detected by adjusting your motion zones.
  • With Live View, you can check in on your home any time through the Ring app.
  • Easily setup your Ring Video Doorbell 2 by connecting to wifi via the Ring app and mounting in your desired location.
  • Powered by a quick-release rechargeable battery pack or connects to existing doorbell wiring.

Ring Video Doorbell 2 is a good DIY peephole camera that provides you multiple features for securing your home. Anyone can easily configure and install this peephole camera. The motion alarm is just the right level of sensitivity, which means it does not capture any false alarms like wind blowing but does capture anyone moving within its range. There are multiple channels to check the live view from- including smartphones, tablets, and we-view for incompatible devices. 

There is 60-day storage for missed events and recordings. This, however, comes with an affordable monthly fee. The night-vision capabilities are also good and it captures visuals from almost total darkness. The only major issue is that you will face issues in checking the Live View on a cellular connection- it requires a fast internet connection to show the video in real-time, but that is acceptable. Overall, this is a versatile and reliable addition to your home’s security system without any complicated tools or software.

Pros and Cons

  • Easy to install and configure 
  • Motion-sensing alerts
  • Ring doorbell can be connected to Alexa for alerts
  • 60-day video recording
  • Motion-sensing has a 1-2 second delay in recording 
  • Mobile interface for viewing needs improvement 

5. Eufy Security – Detailed Review

eufy Security, Wi-Fi Video Doorbell, 2K Resolution, No Monthly Fees, Secure Local Storage,Human Detection, 2-Way Audio, Free Wireless Chime-Requires Existing Doorbell Wires
  • A Crystal-Clear 2K Image: High Definition 2560 x 1920 resolution, combined with our advanced HDR and Distortion Correction, ensures video is recorded in 2x the quality.
  • No Hidden Costs: Designed to protect your home as well as your wallet, eufy security products are one-time purchases that combine security with convenience.
  • Respond in Real-Time: Speak directly to anyone who approaches your front door via two-way audio. Tell your friends to come round the back or that you have just run out to get some milk.
  • The Alerts Which Matter: With AI technology and our sophisticated algorithm, the camera intelligently detects body shape and face pattern. Ensuring you are only alerted when a human, and not a stray cat, is at the door.
  • Free Electronic Chime Included: Supports 8 fun and holiday-themed ringtones and adjustable volume level. Note: The doorbell requires Existing Doorbell Wires at 16-24 VAC, 30 VA, or above.

Eufy gives you not just a digital door peephole camera, but a complete security solution for your home. There are no hidden costs or subscriptions associated with this, so one purchase is all you need to do. It has 2-way audio along with high-quality images with distortion correction as well as HDR. The set up is easy and it has a lot of helpful configurations done by default. For instance, with every alert delivered in near real-time to your mobile or tablet device, 3 seconds of footage before it is also captured.

Eufy is also in the process of applying AI, so the camera automatically detects if there are stray animals like a cat and tries to not send an alert for them. You also have the feature to customize the specific areas where you want motion detection, which can be handy to avoid false alarms. 3 pre-recorded instant responses allow you to quickly share instructions to delivery personnel, etc., something that no other system offers. Overall, this is a good feature-rich security solution without any hidden charges.

Pros and Cons

  • One-time purchase, no subscriptions/other costs
  • 2k recording with HDR 
  • Alerts use AI to filter out stray animals, etc. in motion detection
  • Near real-time push notifications
  • Expensive
  • No battery. Needs an uninterrupted power supply

6. Arlo Video Doorbell – Detailed Review

Sale
Arlo Video Doorbell | HD Video Quality, 2-Way Audio, Package Detection | Motion Detection and Alerts | Built-in Siren | Night Vision | Easy Installation (Existing Doorbell Wiring Required) | (AVD1001)
  • See more at your front door: See a person from head to toe or a package on the ground with a 180- degree viewing angle.
  • See a clearer picture: Detailed video in HD with HDR ensures you see the details even in low light or bright conditions.
  • Respond quickly: Hear and speak to visitors at your door with clear two-way audio or respond with pre-recorded quick reply messages when you are busy.
  • Alerts that matter most: Receive notifications when motion is detected for people, packages, vehicles, and animals with included 3 months trial of Arlo Smart.
  • See events before they happen with Arlo Foresight: See video prior to every motion-triggered video recording, so you never miss a moment

The Arlo video doorbell is equipped with one of the most advanced cameras in the range, especially in terms of night-vision capabilities. If you have existing wiring on your doorbell, installing it is simple. Do note that it does not have any battery backup so you will need a constant electricity supply. It automatically provides alerts when motion is detected, but you need the Arlo Smart subscription to get this beyond the first 3 months. Video prior to the motion sensors being triggered is also easily accessible.

The built-in sirens can be triggered manually or automatically in case of specific events, which can be a good deterrent. Videos can be stored in the cloud or base station, depending on your preference. It is compatible with any voltages between 16V-24VAC, but you also need a 10Va transformer with that- which is not supplied and must be purchased separately. Apart from these 2 extra costs, Arlo does provide a value-for-money solution that you can depend on.

Pros and Cons

  • Excellent night-vision capabilities
  • Integration with any smartphone, tablet and Alexa device
  • Resistant to tough weather conditions
  • Built-in security siren
  • Need extra subscription after 1st 3 months for live-alerts and cloud recording
  • Needs an extra 10Va transformer to install

7. Zerone 3.5″LCD HD Screen Peephole – Detailed Review

3.5"LCD HD Screen Peephole Viewer Digital Door Eye Viewer Camera 480×320P Image Resolution 120 Degree Wide Angle Home Security System
  • 【HD Outdoor Camera】 --- this peeple viewer camera provides up to 480×320P image resolution, allows HD display, enable you to know visitor information timely and clearly. Mini outdoor camera, 24 hours monitoring, protect your family all day and night.
  • 【Hidden Style Peephole with Wide View Angle】--- this digital peephole looks very similar to normal optical peephole, thus it can avoid getting involved in troubles concerning invasion of privacy; 120 degrees super wide viewing angle provides you a further viewing vision, which means better security service
  • 【TFT Color DISPLAY & One Button Start】--- 3.5 inches LCD Color Display Screen, with HD resolution of 480 x 320p, shows images or videos clearly and smoothly. It is more convenient and quick to use, and will automatically change to standby state after 15S with no operation, and can be started with one press at any time, which is very suitable for the elderly and short children to operate and see situation outdoors clearly
  • 【Portable and Simple Design】--- The outdoor camera is made of high quality zinc alloy, which is not easy to be damaged; the indoor mainframe with beautiful coating plastic cover, so light and slim
  • 【Convenient to Use 】--- Easy to install, very easy to replace your old optical peephole with this digital peephole viewer kit, no extra screws needed. It's simple but practical home security device for you.

If you are looking for a digital peephole that is not visible on the outside and fits your budget, then this hidden peephole camera will fulfill your requirements. It looks just like a normal peephole but packs in a 480x320p resolution with HD display and wide-angle capture. Thus, you can view who is at the door without risking any privacy concerns. You get a 3.5-inch LCD, which is the only device you can view the camera on- it is not compatible with any other device.

This is a simple and portable device that does the job of a digital peephole- nothing more or less than that. You can easily install it without any screws or complicated tools. Replace the existing peephole in the door and you are done. There is no motion detection or alerts pushed to your smartphone. If you need a solution that elders and children can use without any complications, then it may be exactly what you need.

Pros and Cons

  • Affordable and easy to configure
  • Digital peephole is hidden and not visible from outside
  • 120-degree wide viewing angle
  • One-press start on viewing screen
  • No alerts or motion detection
  • Cannot view camera on smartphone/tablets

Peephole Camera Buyer’s Guide

Since it is a matter of your safety and security, you must consider every factor before making a decision. Our list of the most important considerations while buying a peephole camera will help you do just that so you can have a tested and reliable peephole camera in your budget. 

Primary Requirement

What is your primary requirement? Do you just want a digital peephole so that you can see who is on the other side of the door? If yes, then a simple peephole camera may do it for you. These come with a separate screen that shows you who is on the other side of the door. 

However, if you want more features like motion detection, integrated sirens, connectivity, and alert on your smartphones and devices, then you need to go for a more advanced digital peephole camera. 

Ease of installation

As you plan to install the camera yourself, you must check how easy it is to install before purchasing it. Does it require any special tools, parts, etc? Are they provided with the door peephole security camera or do you need to purchase it separately? Check if it is a simple installation in the existing peephole or does it require any complex wiring. 

Power Source

You can get a peephole video camera that is connected to your existing doorbell wiring or one that is battery operated. In the first case, ensure that it has either a backup battery or some mechanism by which power is supplied to it uninterrupted in case of an outage in your home. In case you go for one that is operated only by a removable battery, have a spare set to minimize downtime. 

External viewing 

While certain devices can connect to your PC or smartphone, some come with a dedicated device to view at the door. Connectivity to smartphones and PCs can be handy in keeping an eye on who is at the door even when you are away.

Two-way communication  

Two-way communication allows you to see and speak with the visitor. This is a good way to politely ask unwelcome visitors to leave, instruct delivery personnel to leave items at the door, etc. 

Knocking/Doorbell Sensors

Similar to motion sensing, these get activated when someone rings the doorbell or knocks on the door. Such sensors are also equipped to capture video a few seconds before the event.

FAQ

How does a peephole camera get power?
Most peephole cameras get power through the doorbell power source. However, you can also set up battery backup or use rechargeable batteries as the power source.
Will motion-sensing get triggered by wind and small animals?
A quality motion-sensing camera does not get triggered by wind. Certain cameras also have AI that can learn and avoid triggers by small animals and plant movement due to wind.
Can I use a peephole camera to talk to a person at the door?
If the camera you choose has 2-way communication, you can use it to speak to the person at the door as necessary.
How do I know what triggered the motion-sensing event in the camera?
All motion-sensing cameras capture videos 3-5 seconds before the motion-sensor alert is generated so that you can know what/who caused the event.

Conclusion

A  peephole camera for an apartment or any type of home is one of the simplest yet highly effective security measures that you can take. Not only does it act as a way to keep an eye on your home, but it also deters anyone from breaking in or causing any type of harm to your property. All you need to do is consider the important features and requirements before buying once, which is what our guide is all about. 

Right from checking who is at the door to keeping an eye on your home when you are away to safeguarding children and the elderly when they are alone at home, a door peephole camera serves several purposes. The best part of it all is that all the security cameras that we reviewed are simple to install- you do not need a professional and can easily make a quick DIY project out of it. So what are you waiting for? Pick one and secure your home and family today.

Peephole Camera: Bestsellers

SaleBestseller No. 1
Ring Peephole Cam - Smart video doorbell, HD video, 2-way talk, easy installation
  • Upgrade your door’s peephole with a 1080p HD video doorbell that enables you to see, hear, and speak to visitors from anywhere.
  • Get alerts on your phone, tablet, and PC when anyone knocks on your door, presses the doorbell button, or triggers the motion sensors.
  • Peephole Cam is easy to install and comes with all the tools you need to replace your peephole in under 5 minutes; no wiring or drilling required.
  • Connect your Ring doorbell with Alexa to hear announcements on your compatible Echo device when your doorbell is pressed and see a live view of your camera if you have an Echo device with a screen. Talk to visitors by saying “Alexa, talk to the front door.”
  • Advanced Motion Detection lets you easily adjust the built-in motion sensors to focus on and detect what’s important to you.
Bestseller No. 2
Brinno Peephole Camera Home SHC500 Security Long-Lasting Battery DIY Install LCD Screen Black - 12mm Size
  • Concealed Design: View through LCD screen and save images of visitors without alerting them, giving your time to decide whether or not to open the door.
  • DIY Install: The SHC500 is attached to your pre-existing peephole meaning no special tools are required. Installation takes seconds!
  • Long Lasting Battery: Running on merely 4AA batteries, its high efficiency battery life provides the peephole camera with energy for up to six months (approx. 3,000 triggers).
  • Guarantee: Your satisfaction is important to us, which is why we provide customers with a lifetime warranty. Not happy with your purchase? With our 30-day money back guarantee, return your camera for a full refund no-questions asks.
SaleBestseller No. 3
Ring Peephole Cam with Rechargeable Battery Pack
  • Upgrade your door’s peephole with a 1080p HD video doorbell that enables you to see, hear, and speak to visitors from anywhere.
  • Get alerts on your phone, tablet, and PC when anyone knocks on your door, presses the doorbell button, or triggers the motion sensors.
  • Peephole Cam is easy to install and comes with all the tools you need to replace your peephole in under 5 minutes; no wiring or drilling required.
  • Connect your Ring camera with Alexa then enable announcements to be alerted when motion is detected. Talk to visitors through compatible Echo devices by saying “Alexa, talk to the front door”.
  • Works with Ring Video Doorbell, Peephole Cam, Stick Up Cam Battery (2nd and 3rd Gen), and Spotlight Cam Battery
Dmitry Leiko
Author and Today's Expert

Hi there! Dmitry Leiko here, I am the author of the article you've just read, and I write reviews for Expert Bestazy, how you've might guess. I'm passionate about a lot of things, from fishing to reviewing the newest gadgets, I especially adore writing and doing this thorough reviews on absolutely different products, as I've tested a lot of them myself and every time doing long research and advising with experts in a particular field to find the best of the best, I hope you'll find good use of these reviews! :)

Dmitry Leiko