The E3S-AR81 is a diffuse reflection photoelectric sensor manufactured by Omron. It is designed to sense the presence of an object using a sensing beam detecting up to a distance of 800 mm with a sensing head of 4 mm in diameter. It has an insulated plastic housing and a standard threaded screw-on mounting bracket. The E3S-AR81 can operate in a variety of conditions including high temperature and humidity, vibration, and shock. It also features an LED operation indicator, a polarity mark, and a wiring fixer.