Magnetic Proximity Switches
Reed switches are a class of switches used in certain areas of electronics. These devices consist of a set of magnetized switch contacts inside an evacuated glass envelope.
When a magnet is brought near the glass envelope, the switch contacts either move apart or come together, depending on Which pole of the magnet is nearest.
Some reed switches are normally closed (N.C.), so they open when the magnet is preset.
Others are normally open (N.O.), so they close when the magnet is close.
Still. others are single pole, double-throw (SPDT) types, so they provide both N.C. and N.O. functions.
In the magnetic proximity sensor shown in figure, the object being detected is fitted with a permanent magnet. When the magnet comes close to the reed switch, it causes the switch to actuate and send a signal to the electronic circuits monitoring the process.
How this reed switch used in intruder alarm systems?