Infrared proximity sensor, Sharp. Part # has an analog output that varies from 2.8V at 15cm to 0.4V at 150cm with a supply voltage between 4.5 and 5.5VDC. The sensor has a Japanese Solderless Terminal (JST) Connector. You can buy the related pigtail or soldering wires directly to the back of the module.
This sensor is great for sensing objects up to 5 feet away!
Another way to connect the sensor if you don't have the right connector at hand:
The following is the sensor output when a person walking from 9 feet to 2cm.