Using a PLC for Home Security?

Your question is rather vague and covers a large subject so let me ask a couple of questions.

Do you already have a PLC and I/O on-hand that you want to use? If so what is the model?

Do you have an existing alarm system or is the PLC going to be the system or do you want to integrate the PLC to an alarm system?

Are you looking to do a professional level installation or is this a simple weekend warrior project?

As said above: your question is too vague, but here is one way.

1. Wire input to front door.

2. Wire output to solenoid.

3. Connect actuator to trigger of shotgun.

In the name of safety I will not provide the exact ladder logic, but it may look close to this ---| |--------( )

4. Contact good lawyer to defend against murder charge that will result from burglar setting off the "alarm".

5. Practice this line: "Not tonight Bubba, I have a headache."

There is a much better way. Instead of connecting the output to the trigger of the gun connect it to a door latch that opens the door of the room where you keep a couple of Doberman Pincers. It also helps if you accidentally forget to feed them till you get home.

If you are worried about the legal part just put up a sign that says something like this

A pair of Doberman Pincers live here too!

That way you are not saying they are dangerous but the average idiot burglar gets the picture.

Actually you can use a PLC as the controller for a burglar alarm but the problem is you cant monitor for tampering or damage like you can with a burglar or fire alarm system.

With security alarms the control unit expects to see a certain resistance commonly 600 Ω or 1200 Ω. With a burglar alarm. If the resistance increases above this value it indicates an alarm condition while a lower resistance indicates a fault. With fire alarms it is the other way around.

There are several reasons for this but primarily if a burglar is trying to tamper with an alarm system it is more likely to go open circuit when the cable is cut while in a fire the opposite is true when a cable is burnt.

Most PLC inputs can't look for a specific resistance and give you both an alarm and fault indication they can only say that the circuit is open or closed. You could however build a small circuit that could do this but it would need two separate inputs on the PLC to give you the three state result.

On the other hand you could just use the PLC to detect an open or closed condition in any of the sensors but this will not be as reliable and secure as the looking for a specific resistance. You will also not be able to clam that you have a security system as it doesn't comply with many of the standards.

choice is your

Being that PLCs are designed for use in industrial equipment, they lack the proper certifications for use in residential applications, vis-a-vis RFI/EMI emissions per FCC standards in the US, CE standards in IEC conforming countries. Technically then, your answer is no, but you can do whatever you want...