Thwarting bike thieves with alarm, strobe lights

Thread Starter


Joined Jan 1, 2022
I have an old garage with a pull up door where I store some expensive bikes. It's a pain in the neck to lock it and even when I get it locked, the padlock can easily be cut with boltcutter. I'd like to put a magnetic contact sensor on the door, such that when it is opened between the hours of about 10pm and 7am, a loud alarm sounds and strobe lights flash. Our bike thieves are not particularly sophisticated. I'm sure the alarm and strobes would scare them off. Plus our bedroom is close to the shed.

I'd like to be able to power the alarm by plugging it in to an outlet in the garage with a plain old analog timer that will supply power to it between 10pm and 7am. I don't want anything battery powered or wireless. I don't want a smart system that connects to my phone. I want to be able to set it up, set the timer and forget about it.

I can't seem to find any ready-made products online that do this and I have no idea what to Google to get some guidance. It would be great if someone could tell me what terms to Google or what products to look up. I'm pretty handy but haven't done any electrical. Thank you in advance for any help.


Joined Dec 31, 2017
You need a timer
12 volt power supply 5 amp
Relay module
Garage type magnetic switch
12 volt siren
12 volt strobe
Won't need to build anything
Basically connect the components
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Joined Sep 24, 2015
I always wanted to make an alarm system with - instead of an alarm - a recording of a woman screaming bloody murder. I'm sure that'd make the would be thieves swallow their back teeth when the sound of a woman screaming bloody murder (from an old movie).

No, I'm not asking how to build such a device, just making a comment about alarms that scare thieves. You could just as easily use the sound of vicious barking dogs. But an alarm and strobe light will be more than sufficient.

Audioguru again

Joined Oct 21, 2019
Unsophisticated thieves? Where are you so I will never go there?
Here, the thieves only rob banks and there are no banks on my street. If somebody has a noisy alarm then the police will remove it and charge the owner for disturbing the peace.

Audioguru again

Joined Oct 21, 2019
I did some work in downtown Phoenix and stayed in a hotel there. The people were civilized.
In the south, maybe criminals sneak across the border.
I stayed in Mexico twice and I did not see any criminals there either.


Joined Jan 23, 2018
If you use a 120 volt bell and an AC powered strobe then all you need is a mechanical switch inside the door. And if you want a really big racket, ten of the 12 volt car horns in series across the mains when the switch is closed. But with the horns in series the cases of 11 of tem will be above ground and be a serious shock hazard while they are powered. But they can be spread around the garage up high on the walls and the racket will be panic inducing, especially if e alarm bell is also clanging.


Joined Dec 2, 2017
And I guarantee if the bikes are not locked you will get a smash and grab type of burglary.

The only time an alarm system works, is after setting the thing off, it is difficult to steal something within a short period of time.

Ask me how I know.


Joined Jan 23, 2018
Of course you can also add a single chain, or thick steel cable, anchored to an eye-bolt screwed into a garage structural part, or into an anchor in the floor. Not totally unbreakable, but will take a few minutes to break. Threaded through the frame opening of all the bikes. Breaking or cutting that will take at least a minute, and if the alarm system is at least 120 Decibels it will provoke a panic among the bad actors. Flashing strobes also make it harder for them to focus. AND if the alarm triggers before the door is opened very wide they might not even get inside. And the good ting about such an arrangement is that if it is triggered accidentally no injuries result. An actual farm livestock fence charger hooked to the cain restarining the bikes could seroiusly slow the bad actors a bit more. Painful but not lethal.

Audioguru again

Joined Oct 21, 2019
The thieves sneaked across the border and stole bicycles in southern Arizona.
I was going to ask what will you do if your alarm goes ringing but I forgot, in USA everybody has a gun.