Electronics > Beginners

alarm going off when connection breaks?

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ddmeltzer8:
Hi.
I would like to make an alarm that goes off if the connection breaks,like if i wire something and someone grabs it and take it.Just for the alarm to go off.
Sorry if this is too vague.Im pretty green.
I have this sign that gets moved around some times.And i want to be able to hear when someone takes it.

Thanks in advance.

ArthurDent:
We really need more information like is the sign powered and how far is it from where you will be.

One way to accomplish what you want would be to modify and use an alarm designed for other applications. Here is a medical Alzheimer's or wander alarm you put on a door to alert when a person opens the door to leave and the remote sounder can be up to 150 feet away.

https://www.alzstore.com/door-chime-alarm-add-on-p/0068.htm

I don't know what is available in your area but there are many types of alarms with remote sounders for intrusion alert available. Most of these use a magnet that when moved away from a sensor will trigger an alarm and you would have to modify it so when your sign is moved it would move the magnet. With any of these sensors if they are to be used outside you would need to protect them from the weather.   

t1d:
Can you dig a hole, drop in the end of a chain, fill it with concrete and lock the chain to the sign? Otherwise, Arthur is right, about adapting an existing alarm type. There are lots of movement/motion sensors... Some for bicycles...

As for you own circuit...
A mercury switch, to detect movement... that triggers a latching switch circuit... that sounds a buzzer, flashes lights, etc. Could be run off of a nine volt battery. Just a few components would be needed. The vandal will drop it, as soon as it sounds.

If you want to get fancy, you could use an Arduino, with a BlueTooth/Wifi/etc. notification.

NivagSwerdna:

--- Quote from: ddmeltzer8 on November 06, 2018, 02:00:45 pm ---I would like to make an alarm that goes off if the connection breaks
--- End quote ---
Simplistically that is the same principle used in many electronics goods shops here... there is a loop that passes through tags on the goods and if the wire is broken the alarm goes off.  A relay powered by the loop and an alarm on the normally closed contacts would do it?

A bit like these?  https://www.insight-security.com/retail-loop-alarm-systems

Brumby:

--- Quote from: ddmeltzer8 on November 06, 2018, 02:00:45 pm ---I would like to make an alarm that goes off if the connection breaks,like if i wire something and someone grabs it and take it.Just for the alarm to go off.

--- End quote ---

This is really easy - as far as the alarm side is concerned.

What IS going to be the main factor in the design are the physical details.  Such as: Where is the noisemaker going to be located with respect to the sensor?  Will the system need to be battery powered?

As far as a sensor is concerned, you can have two wires that get separated or a magnet that gets pulled away from a reed switch.  There are lots of alternatives.

If you give us a bit more detail on exactly how things are arranged and how you would like it to work, we can offer you much better suggestions.

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