I tried one of these out and it worked so well I've bought another half dozen. It wasn't obvious at first but these sensors actually measure 3 values - motion, light luminance (lux), and temperature (celsius). By measuring the luminance the Philips Hue app cleverly only turns on lights when there is motion *and* it's night time. Installation using the Philips Hue app was too easy for words - it even asks you which light to control and sets up all the triggers and values, so it just worked. As a bonus I now also have the temperature of the room on my iPhone.
The lights on my stairs and in the entrance now turn on automatically. No more fumbling for light switches in the dark while carrying bags. But didn't have to pay an electrician $$$ to install, just stuck one of these to the nearby wall using the magnetic attachment.
Also works great in the Elgato Eve app and Apple Home app.
Change the way you control light at home with the Philips Hue Motion Sensor. Light up a room simply by walking in and control the intensity by the time of day, such as a gentle, warm nightlight to help you navigate your home at night. Battery powered, wireless, and installation free, this Hue Motion Sensor requires the Hue Bridge (sold separately) to work, connecting to your Hue system with control via the Philips Hue App. Place it anywhere in your home including your hallway, bathroom, kitchen, and more. The integrated light sensor saves energy by detecting when rooms are vacant and automatically turning off lights. Make it part of your Hue home lighting system with Hue accessories (sold separately) such as the Hue Tap or Hue Motion Sensor. Control by voice with Amazon Alexa, Apple Home Kit, and Google Assistant. Connect it with your Nest or Samsung SmartThings system for smart home control. Each kit includes one Hue Motion Sensor with two AAA alkaline batteries, a magnet, screws, a manual, and a two-year warranty.