A reed switch consists of two magnetic
contacts in a glass tube filled with protective
gas: When a magnet comes close to a reed switch
the two contacts become magnetized and attracted
to each other allowing an electrical current to
pass through. When the magnet is moved away from
the reed switch the contacts demagnetize,
separate, and move to their original position.
Reed switches are very reliable and last as
long as 3 billion operations if used properly.
They are designed for low currents. High
voltages applied to the contacts may cause a
spark, which may weld the contacts together.
Please look at the following website:
reed switch motor