Handy tool for checking the working distance the reed sensor is from the magnet or just making sure the parts are positioned and working correctly once installed.
Simply plug the reed sensor into the unit and switch on. As the magnet is brought closer the green light will switch off indicating a door being closed. As the magnet is moved away from the sensor the green light will come on indicating a door opening. Batteries included. To assist, download the Reed Sensor and Positioning Sheet in Brochures here.