Flush Contacts

These are probably the most widely used contacts in alarm systems. A typical application is seen below. The reed is fitted into the frame section and the magnet into the door itself. When closed the contact is concealed making it more resistant to tampering and accidental damage than the surface mounted contact.
Fitting these contacts is not an easy task, care must be taken in ensuring the contact and magnet are in line, that is, the magnet is close enough to the contact to close the reed when the door is shut. Another point to mention is that on very close fitting doors the face plate may prevent closing, if this is the case then the contact must be recessed so that the face plate is flush with the surrounding surface.

Fitting Flush Contacts

Here we see a door frame to be fitted with a flush contact. First a 20mm hole is drilled, this should be deep enough to accept the contact and the wiring at the back. A 5mm hole is drilled and the cable is passed through this to exit from the first hole. The cable is then stripped and connection is made to the contact. The contact is then pushed into the hole and secured to the frame by screws or tacks.

This then leaves the magnet to be fitted into the door, make sure it is in line with the contact and the door closes correctly.