Seeed grove physical sensor modules seeed studio 101020038 the grove magnetic switch from seeed studio contains a dry reed switch that can be activated by a permanent magnet or electromagnet the normally open switch is connected to a digital line and has a pull down resistor giving a logic 0 signal when a magnet approaches the contacts close and the output goes to a logic 1 seeed provide technical documentation example projects and software libraries on their product pages if you requ