"They are normally closed wired.
Quite often a series resistor is used somewhere along the line, and sometimes very near it in the reed relay casing to avoid a tamper and bypass via an external wire ( zero omhs ) across it's terminals.
Values are around 3.3, 3.9, and 4.7 kOhms.
If say three reed switches are in series on a 4.7 kOhm circuit, best practise is if space allowes to put a 1.5 kOhm resistor in each reed switch casing if space allowes.
The loop will be sensed at 4.5 k Ohms by the alarm unit. You can can put a 200 R in the alarmbox to match exact 4.7 kOhm for the cct concerned."
RODALCO, has it right, anything less then full supervision, is not security, it's no more then a noise box, the so called basic security systems are usually sold by mass marketers with one objective, create large monthly revenue streams, not to provide security, if you are installing security seytems, be sure to check your liability coverages, and your contract, security installations, are more involved then just running wires and contacts, give some thought to the liability issues.
