Security alarm question

nmm

I want to connect an existing alarm system with a siren to a new gsm-dialer system.
The siren has an output of 9-15v 745 mA; can I use one of the reed-switches which are probably NO and connect a relay to siren that operates a relay which activates the reed-switch which then signals gsm base-station?

I would have to connect the relay to the reed-switch. I am not sure what type of relay I would need to power the relay-coil from the siren-output given the v and mA of the siren-output.. Thanx for your help.

T Chap

Most alarms have a contact closure on it for external triggering. Have you seen any contacts you can use? The siren idea seems convoluted.

LoopyByteloose

I suppose a 12VDC rated relay coil might working in parallel with the siren load, but can a reed switch hold up?
The 12VDC relay coil is usually about 60ma.

It might be wise to include a flyback diode across the relay coil to keep the reed switch working longer.

Wiring it this way really doesn't offer you any opportunity to test the system in a silent mode and without actually calling whomever your are calling. A test that the alarm circuit is active and ready before including it in the noise making and calling allows you to avoid embarrassing false alarms when one window or door is left open and overlooked.

You might as well have the reed switch drive just the relay coil and have the siren and other stuff switched on by the relay. Many relays have two switches with two on positions, called DPDT relays. You could even have one switch provide 12 volts to the siren and another provide 3.3v or 5v to your dialer device.

nmm

TChap and Loopy,
Thanx for your replies. I should explain further what I am trying to do. I have an existing alarm system hardwired with a siren; no monitoring. I want to connect a gsm dialer activated by the alarm-siren. The alarm-system has a control box with a telco output T(ip) R(ing) T1(ip) R1(Ring) and 2 other leads for line tamper. Of course the system is an old c&k236 security system. I want to connect a gsm-dialer that is siren-activated; when the siren is sounded it will close the circuit on one of the fortress wireless radio transmitted window sensors (modified with the relay) which will activate the radio transmission circuit inside the window-sensor and send an alarm trigger to the fortress-gsm-dialer.

I can not connect the gsm-dialer to the c&k telco line because (of course) it is made only for central-station-monitoring with separate handshake and data protocols which would take forever to figure out. I just need something which is NOT very sophisticated but will still work.

So I still need a relay which will replace the siren but not damage the c&k control box by connecting it to the relay coil instead of the coil to the siren. The relay coil will be energized by the siren 9v 745mA and close the window-sensor contact and then signal the fortress-gsm-dialer and dial out to the cell phone to notify of an alarm trigger. Have I explained enough? Thanks for your replies. nmm.

LoopyByteloose

Just consider a few alternative means of deploying the relay. You may end up with a better setup.

Of course, if the siren is being driven by 9vdc, a 9vdc relay might be a better choice. I am not a user of magnetic reed switches as the have bounce issues when directly connected to a microcontroller input. So using a relay may be a wise addition.

kwinn

Taking in to consideration how often the relay will be activated (not often), you should be fine with a reed relay. If a 9V reed relay is difficult to find you can use a 5V or 6V relay with a series resistor.