2.5m 4m barrier Gate & Door Opener Retro Reflective Photocell Photoelectric Sensor Beam Photo Electric Reflector 2M on the box means the cable length of the sensor, not detection range. manual not updated and 4m on the manual is not correct. Retro-reflective sensor for gate opener, boom barrier; for the power supply, there are 110V/220V version and 12V/24VDC version; for the smaller reflective board, the range is about 2.5m; when installing it, make sure no sunshine interferece; Light resource: Infrared LED Strong anti-shock and anti-vibration. Non-contact object detect: Avoid the photoelectric sensor to contact the object directly, protect the inducing component from damage and extend the operation life of the sensor.