Presence Sensor
More sensitive and faster response times
Introduction
Motion Sensors have been on the market for a long time. They are the hallmark of smart home security and automation. More recently, presence sensors have become abundantly available.
Overview
| Feature | Motion Sensor | Presence Sensor |
|---|---|---|
| Detects Motion | ✔️ | ✔️ |
| Detects Static Activity* | ❌ | ✔️ |
| Adjustable Sensitivity | ❌ | ✔️ |
| Can Detect Activity Through Objects | ❌ | ✔️ |
| Power Source | Battery | Wired |
| Price* | $25+ | $35+ |
Justification
Advantages of a Presence Sensor
The primary difference between a motion sensor and a presence sensor is how they detect activity. Motions sensors typically use passive infrared (PIR) while presence sensors use mmWave radio (RADAR). Ultimately RADAR is more sensitive, though it does have a slightly higher power requirement.
Motions sensors do exactly what you expect them to, they detect if there is motion. At a basic level this is perfectly fine. You walk into a room, and it can trigger the lights to turn on. However, if you are in the room and not moving much the light will likely turn off on you. This leads to setting a long time period after movement stops to ensure that the room is actually empty. The idea is that a person should move within the time period, and you have to do some guess work to determine how long that period might be. This can be as much as 10, 20, or even 30+ minutes; during which time the light will stay on even if nobody is in the room.
Presence sensors eliminate the timing problem because they are able to detect if you are in the room even if you are not moving. You can reduce the delay after motion stops to as little as 30 seconds or less. This single detail is why I strongly prefer presence sensors.
Another cool feature of presence sensors is that they can detect activity through other objects. This means placement is less of a concern because they will not be blocked. I placed one of my sensors so that is behind a door when the door is open. This can mean the sensors pick up activity in an adjacent room though, which is why they also typically allow you to adjust the sensitivity and detection range.
Disadvantages of a Presence Sensor
Not everything about presence sensors is better than motion sensors. Motions sensors are low power devices and can run for years on battery. The higher power requirement for presence sensors that I mentioned earlier means presence sensors don’t run on battery. To be clear, their power consumption is only a few watts, but they do require an outlet which may limit their placement. Fortunately, they are designed to work closer to ground level.
The extreme sensitivity of presence sensors also has some drawbacks. If the sensitivity is up too high, they will pick up motion that you might not even be able to see, leading to false positives. If you have a ceiling fan running then you can pretty much guarantee that the device will detect motion, eliminating its usefulness entirely.
A final disadvantage of Presence sensors is that they are typically a little more expensive. However, they usually come with a luminance sensor which can help to make up the difference. If you pick up a motion sensor with luminance, you’ll find the devices are similar in price.
Recommended Products (paid links)
Motion Sensors
Philips Hue Motion Sensor: High quality multi sensor that boast motion, illuminance, and temperature sensors. It can be paired with a Hue Bridge, or directly with a Zigbee Hub like the Hubitat Elevation.
Generic Zigbee Motion Sensor: No fancy features. Just pairs with a Zigbee hub and detects motion.
Presence Sensors
Linptech Human Presence Sensor: An effective presence and illuminance sensor. I purchased the Zigbee version. There is a Wi-Fi version as well that I have not tried. I have mine connected to Hubitat Elevation and it has been working reliably.
Moes Human Presence Sensor: Same as the Linptech presence sensor, just with a different logo.
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