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Can anyone think of any mechanical sensor gadget that I can put on top of the door lock above to detect if it gets opened? In my place, robbers open car doors during traffic and steal or hold up passengers. So I need to make sure the door lock detector would buzzer if it is open or defective because it is at the back seat right side which I can't see.

  • Welcome to Motor Vehicle Maintenance & Repair! – Pᴀᴜʟsᴛᴇʀ2 Oct 24 '18 at 23:25
  • What year, make and model of car is this? Does it have power door locks? – CharlieRB Oct 24 '18 at 23:30
  • It is honda CRV 2004. It has power lock.. but my backseat right lock is old. Two times they already broke. It's dangerous when you think the lock is working and not. I don't want the robber to open it when it gets defective & I didn't know (I don't want to look at it every single moment). So I need to install additional mechanical buzzer sensor to be sure it buzzer when the lock is up. – Samzun Oct 24 '18 at 23:55
  • It sounds like the solution would be to repair the door lock rather than put some sort of buzzer on it. – GdD Oct 25 '18 at 7:44
  • It's already repaired.. but it gets broken again in 2 years or so.. sometimes I only found out after a week and there were times some broken locks were really in open state when parking at mall. – Samzun Oct 25 '18 at 10:10
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In its simplest form, a buzzer detector device you seek could be assembled using off-the-shelf components.

Consider a window alarm sensor switch. One part is a magnet, which is applied to the moving part of the lock mechanism. The other part is the reed switch, which has two electrical contacts.

Connect a wire to a battery, then to a buzzer, then through the alarm sensor switch. From the alarm sensor switch, return to the battery.

You would adjust the magnet and sensor switch to be close to each other when locked. This places the "normally closed" switch in the open position, saving the battery and silencing the buzzer.

When the lock is lifted, the magnet moves away, closing the switch, connecting the battery to the buzzer.

The above description is a quick off-the-top-of-my-head design. One could use more specialized components and have a much smaller assembly but the design concept is the same. I have in the past created a brake light switch for bicycle brakes. When the brake lever is not engaged, the magnet keeps the circuit open. The magnet and sensor for that project had 4 mm diameter components!

  • great idea.. I'd try it.. where did you get the 4mm diameter components or magnetic sensor switch? – Samzun Oct 25 '18 at 2:45
  • Ebay, maplin , radio shack : many places sell that type of kit... – Solar Mike Oct 25 '18 at 4:16
  • @SolarMike Maplin doesn't exist any more: bbc.co.uk/news/business-44606771. And Radio Shack has managed to go bankrupt twice since 2015 (it still has a few stores open, but it closed about 1,000 stores in 2017.) – alephzero Oct 25 '18 at 15:27
  • @alephzero I was last in Maplin in January, but it was a name that sprang to mind... figuring out where to buy stuff is hard... – Solar Mike Oct 25 '18 at 15:29

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