Side-looking Infrared Emitters and IR Detectors.
These simple devices operate at 940nm and work well for generic IR systems including remote control and touch-less object sensing.
Using a simple ADC on any microcontroller will allow variable readings to be collected from the detector.
The emitter is driven up to 50mA with a current limiting resistor as with any LED device. The detect is a NPN transistor that is biased by incoming IR light.

Datasheets:

• IR Emitter (Yellow dot)
• IR Detector (Red dot)

Applications:

• IR Schematic - Basic object detection schematic
• Seattle Robotics - Infrared object detection
• Robot Room - Excellent website with lots of goodies
• Video Tutorial

Sold as a pair, with one Emitter and one Detector.