MPJA.com Reed Switch 100W SPST-NO Pack of 4pcs.

the very small magnetic reed switches are absolutely brilliant small magnetic switches normally used in alarms and other small switching devices these are normally quite small and tiny measuring a total length of 44 millimeters including the wire the glass length is 14 mil and the diameter is only two millimeter there is a whole host of different alarms that use these switches from the small battery ones wireless ones and the normal house contact ones due to the size the read switch can be incorporated in the circuit and box for the small wireless alarms here you can see running on the side of the electronics these switches are normally open circuit but when you put a magnet to them they close so pushing the magnet to and from the switch opens and closes the switch the normal hardwired switch used on most alarms at home has got a bit of a vulnerability when fitting these switches normal