This is the bare infrared sensor used in PIR motion detection modules. The infrared sensor is sensitive to many frequencies in the infrared spectrum so motion detector modules typically add on a Fresnel lens to limit the frequenciy sensitivity to those given off by the human body. However other types of lenses, or even no lens, is possible with the bare sensor. These have applications for temperature or other types of infrared sensing. Stay tuned for tutorials on how to make your own motion detector module.
This device is equivalent to the P4488 and P2288 PIR sensors from Hamamatsu Photonics.