Seeking help from the resident electrical guru's around here haha

[chereck04 10+ year member]

Long story short, my brother in law is a contractor. Last week his trailer was broken in to, thieves made off with $7k worth of construction equipment and copper pipe/wire. Insurance covered everything, but today he got a letter from them saying they're dropping him.

He wants to put an alarm on his trailer but spend as little money as possible (dumb, i know). He went to the yard and pulled two door sensors and four car horns, then showed up at my house and asked me if I had any idea of how to make them in to a working alarm.

Here is what he wants:

Mount a remote switch somewhere on the trailer to arm/disarm it.

When its armed and the door sensors are tripped, it would trip a relay that would keep the horns on, and they would remain on until the switch is turned off (regardless of if the door is open or shut).

I can wire up the door sensors/relays for him, but I have no clue as to what to do as far as a switch goes. I tested the door sensors, when they're extended (door open) it completes the circuit. I could wire them to a relay, but as soon as the thief would shut the door the alarm would stop. Anyone have an idea of what I should use?

Also, I was thinking about possibly just wiring it to a cheap car alarm w/ a wireless transmitter. Any input on this idea?

Thanks in advance,

Ken

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[Sanchito 10+ year member]

good luck brother.

i would say put the switch inline on the power wire that powers everything. if the door sensors get no power, the alarm wont go off.

as far as keeping the alarm going regardless of the door being open or closed, why not just put them at the base of the door, close as possible to where the door hinges? so that even the slightest movement one way or the other will set them off?

 

[smoka 10+ year member]

I could wire them to a relay, but as soon as the thief would shut the door the alarm would stop. Anyone have an idea of what I should use?

Latching relay
A latching relay has two relaxed states (bistable). These are also called 'keep' or 'stay' relays. When the current is switched off, the relay remains in its last state. This is achieved with a solenoid operating a ratchet and cam mechanism, or by having two opposing coils with an over-center spring or permanent magnet to hold the armature and contacts in position while the coil is relaxed, or with a remnant core. In the ratchet and cam example, the first pulse to the coil turns the relay on and the second pulse turns it off. In the two coil example, a pulse to one coil turns the relay on and a pulse to the opposite coil turns the relay off. This type of relay has the advantage that it consumes power only for an instant, while it is being switched, and it retains its last setting across a power outage.

Best way to have cheap security is to get a couple of cheap motion flood lights around the trailer. Pair them with a few fake security cams and should scare away most crooks I would imagine.

 

[Johnny Law.Lulz 5,000+ posts]

I have a Hornet 740T if he actually wants to protect his shit instead of just bein dumb about it. PM me if interested

 

[chereck04 10+ year member]

Best way to have cheap security is to get a couple of cheap motion flood lights around the trailer. Pair them with a few fake security cams and should scare away most crooks I would imagine.

Thanks for the info bud! I might even purchase a few of those fake cameras for my garage haha.

He already has a motion flood light out there. It was broken in to in his driveway, 50' away from his house. I don't know how the hell his wife didn't wake up when it happened.