A reed switch consists of a sealed glass tube containing a pair of ferrous metal contacts. When a magnetic field comes close to the reed switch, the two contacts come together enabling a current to pass through the switch. Most commonly reed switches are used in burglar alarm systems in which they act as window and door sensors.
NEW We are now selling reed switches in the REUK Shop.

Reed switches have many uses in renewable energy generation, particularly with DIY wind turbines. For example a reed switch within a simple electric circuit can be used to count revolutions of the wind turbine for analysis purposes (tachometer). Find out more about reed switch wind turbine RPM meters using a calculator or pedometer here.