The reed contact is a special switch that can be closed (normally open contact) or opened (normally closed contact) by a magnetic field. In combination with a magnet, the proximity of two objects can be detected. For this purpose the magnet is usually attached to a moving object (e.g. garage door) and the reed contact is permanently installed (e.g. garage wall or ceiling). If the magnet then approaches the contact, it closes and the changed state can be detected.
The current state of the reed switch can be easily viewed on the mobile phone with our Sense App and a bridge (e.g. an ESP8266 like the ESP-12, NodeMCU etc.). For example, with an Android smartphone, iPhone or even the Apple Watch you can check from anywhere and at any time whether the garage door or a window is still open. This is easily and quickly achieved as a very inexpensive, energy-efficient and individual solution.