A magnetic/reed switch is a switch that closes or opens when in the presence of a magnetic field and is often used in low-voltage circuit applications. They consist of a ferromagnetic material such as soft iron, a thin strip of metal such as copper and a contactor, usually a thin strip of material such as a steel blade. The ferromagnetic material and thin strip of metal can be arranged in a variety of ways, but when the switch is not in a magnetic field all of the contacts remain in place and there is no current flow. However, when a magnetic field is present, the ferromagnetic material and thin strip of metal react and push against each other, thus closing the switch, thus allowing current to flow. These switches are often used in applications such as doorbells, security systems, automotive ignition systems, and air flow sensors. They are also simple, reliable and cost effective.