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Arduino intruder alarm modification Answered

We have a professionally installed burglar alarm system that dials out (over a dedicated landline) to a monitoring station when an intrusion is detected.  I'd like to modify it to send us an SMS (via the mobile phone network) and/or email (via wi-fi on a different landline) as well, just in case the phone line is cut, and to make sure we get notified immediately - the monitoring station tries to call on the landline first, then it calls our keyholders and the police, which all takes time.  If I'm 5 minutes away and the alarm is triggered, I'd like to know straight away so I can rush home.

The alarm company have quoted a huge sum to make this change, because an updated control control panel would be needed to deal with the texting/emailing.  I can't go cutting into their system or it will invalidate the maintenance contract, so I need to pick up when the alarm is triggered without any physical connection.  Short of remotely detecting a current in the cable to the siren (a 12V DC signal, so how would I detect that?) it occurs to me that using Arduino to listen for the siren might be the best bet.  But I'm an Arduino beginner and I have no idea whether it would be better/easier to detect a noise over a certain threshold - the siren is very loud, but the noise from the adjacent road can be pretty loud too - or to try and detect the particular sound frequency of the siren. 

All suggestions gratefully received. 

Discussions

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Qwertypat
Qwertypat

3 years ago

Hello Lass, just a thought, how about using induction?

Perhaps, if you wind part of the wire to the siren around some metal core like a short piece of metal pipe, wind a second copper wire around the same metal and connect that secondary wire with its both ends to ports on the Arduino. You should be able able to pick up (small) electric current passing in the second wire, caused by magnetic induction.from the primary wire when the siren sounds.

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Yorkshire Lass
Yorkshire Lass

Reply 3 years ago

Thanks for the suggestion. I doubt there's enough slack in the siren wire for more than 1 or 2 turns around a very slim core, and that's not going to produce much of a signal. I might give it a try but I think I'd be better off trying to detect the sound, if I only knew how.

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Qwertypat
Qwertypat

3 years ago

to envision:

coil.PNG