Vibration Sensors (Accelerometers)
In addition to the regular motion sensors, there are more expensive ones that also include vibration sensors. These are usually marketed as “multi sensors.”
Different ones will have different Added features. The vibration sensor itself will be used to detect when a large appliances running, like a washer. When there’s a knock or collision of some kind. Or when the sensor itself is moved, which is often described as a “tamper alert” if the device is marketed as part of a security system.
This last feature can also be used as a tilt sensor. One popular and very cool project is to put one of the sensors inside a wooden cube and then have each side of the cube trigger a different home automation event. Lots of variations on this in the community.
The fibaro multisensor is very small and intentionally looks like a colored eyeball. Some people love this look, some find it creepy. Motion sensor plus temperature, light, and vibration. Its vibration sensor is used as both a tamper alert and an earthquake detector.
The Aeon Labs multisensor includes a lux sensor. It’s rated for outdoor use, but only if you disable the motion sensor, as it’s very prone to false alerts when outdoors. Still useful for light and temperature detection. Also a popular indoor motion sensor.
The SmartThings multisensor is very unusual in that it combines an accelerometer (tilt sensor) with a contact sensor. So it’s a two-piece device. It’s particularly popular as a garage door sensor where you want to distinguish between four states: open, Opening, closing, and closed. It does not detect motion of other objects nearby, but it does detect its own motion as its position changes. Also popular for the mood cube projects.