Aeon Labs MultiSensor 6 is my favorite little sensor. First and foremost, its a very good passive inferred detector. I use a bunch of them to secure different areas of my home. They are easy to install and have to option to run on batteries or be plugged in. The batteries last months under normal usage. The real selling point for these sensors is that they are not only for security but they can also be used for environmental control too.
The MultiSensor measures temperature, humidity, light levels, and ultraviolet levels. This is feature incredibly useful when used in conjunction with a Z-Wave thermostat like the 2gig CT100 Z-Wave Programmable Thermostat .
I can get distinct ambient temperatures for each room that has a MultiSensor in it. I can use this information to adjust the temperature of the thermostat depending on what room my family is in or according to a set schedule. Although the total system cost is more than a Nest Thermostat, it has far more capability and its also a whole home security system.
It’s a cool little sensor and quite a good foundation for a home automation project.