Idea for silent alarm…..

A while back I wrote about an idea I had using small solar-powered lights to charge AA batteries. Works well and is inexpensive. Reader “Brad” sent me an email and gave me another idea. Use these lights as a silent alarm.

Here is how it works:

First – a solar light has its post removed as it is going to be mounted to a tree, not stuck in the ground.

Second – look at the solar light and find a safe place away from the electronics to drill a hole for a mounting screw. Drill the hole.


Now – the way this thing works is with the LED pointed outward from the tree(solar part covered) – a piece of tough plastic with a string attached (I like fishing line) is stuck between one end of the battery and the internal contactor. 

The end of the string will need to be attached securely. When someone (or some “THING”) walks and “trips” the string, causing the plastic tab to pull out – the battery will then make a complete circuit and the light will come on (only when its dark out). The sensor that detects light can be covered – but I didn’t really see the point.


Think about all the places these could be put. You can see in the picture above one is by my back fence. How about several of them all along the top of the fence so that if someone crawled over in the middle of the night the light would shine like a beacon? I think that would work well.


By the way – the one you see in the pictures above have been attached to that tree for over 3 weeks and it has sat in the intense sun as well as torrential downpours – still works just fine.

I see this nighttime perimeter alarm set up as inexpensive as well as effective. In complete darkness with no other lights on – it really stands out. Imagine someone standing watch in a window looking over a large backyard and suddenly one of these lights comes on – they could throw on some larger solar lights to illuminate the area to check out what was there. Now – imagine the same situation without this perimeter alarm. Someone could sneak over the fence and unless they made some noise you might have no idea.

Zombies have invaded – see the tripped solar light alarm towards the back of my backyard.

I am working on getting a bunch of these, along with some fishing line, screws, drill bits, and batteries and storing them away in a small tote.

So, what do you think?


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18 thoughts on “Idea for silent alarm…..”

  1. How about in addition to, or in place of the light, a small buzzer? A noise maker would alert you to a perimeter break without the need for intense visual monitoring.

  2. Thanks, I had forgotten about it. I’m going to string some up and see how they work. Hmm… I wonder if deer are susceptible to heart attacks?

  3. Seems like a bit of overkill. You don’t need the solar sensor or charge circuit, just a led and battery and your makeshift trip switch. It is not going to charge set up in this manner so I kinda don’t get it. Easier ways to go about this. Like a few pebbles in a soup can. Regards, D.

    • D.- I can’t imagine it getting much easier. $1 to $3 for the light – mount it and done. No doubt there are other way – possibly with some very inexpensive multi-LED flashlights. Yes – the solar element is not used – but that is OK.


  4. Thank You Rourke. good cheap way of things. Unknown above mentioned a great variation. Daisy chain two or more to actually ‘mark’ a ‘field of fire’. Silent and if gelled red or blue….. unseen by the perps. possibilities possibilities…

  5. And you could even string your tripwires along backyard and have the ends run to a back porch hooked to the lights ,each light labeled as to what part of the yard it covers. A sort of Poor Man’s control room !!

  6. Good in theory, fails in reality. You will not see the indicator in real time unless you are standing guard. If you are standing guard you should have NV and will see them long before they trip an in we perimeter. False sense of security is all I see this giving.

  7. DVC – I believe I stated in the article that someone standing guard would see the light when it came on. Not eeryone had night vision – this is merely one way to skin a cat.

  8. They make solar lights with motion detectors. That way the lights are being charged constantly and the light can be placed anywhere there is sunlight. No need for trip wires that need to be reset.

    • Bob –

      I have experience with with a few models and have found them to be less than desirable in a grid down SHTF situation IF you are not trying to draw attention to yourself. Many of these lights can be set off when a cat, dog, or even a bat passes through its sensor area. Have the light go off multiple times all night would be quite a beacon to anyone in the area – attracting attention.


  9. As a suggestion, you could keep the solar light pretty much in tact, simply modify the clear plastic housing to allow the addition of the your trip wire system, then mount through the vertical riser to the tree. This way, it will charge, give off MORE light and still be fairly weather tight.

    Just my 2 cents.

  10. To offer the opinion that the idea is not a good one because one should have night vision or tin cans filled with pebbles is absurd.

    Some people cannot afford night vision devices. (I have four, last count.) To dismiss the idea because night vision is better is an indication of the smug approach that is all too common among some preppers (ham radio operators, scuba divers, rock climbers, etc., etc. ).

    No one said that tin cans with pebbles could not be used as a security measure in conjuction with these solar lights.

    And to say that they would not be useful because they would have to be monitored dismisses their usefulness during a situation where you would absolutely need to be monitoring a perimeter rather than sitting in front of the plasma big screen watching “Dancing with the Stars.”

    I suppose these same people will next be telling us that trip flares are unnecessary in defensive applications because FLIR is what we should all have.

    We need to encourage innovative ideas that can be carried out on a budget, not suppress the offering of new ideas.

    For those who are interested, simple solar lawn lights are currently and commonly availble at dollar stores in my area.

    I would consider using the entire solar light. Of course, doing so would give an intruder immediate notice that his presence has been detected. A more subtle LED might not tip him off.

    Still, the best way to survive a fight is to avoid one. I am reminded in some ways of the acknowledged usefulness of a “Beware of Dog” sign even if there is no dog. If immediate detection causes an intruder to back off and pursue the “low hanging fruit” elsewhere, IMHO that is better than waitng for the intruder to continue forward unaware that he has been detected and to have him in close proximity before serious (which is to say, deadly) defensive measures are initiated–and then take one’s chances on the outcome.

    Using cheap devices rigged such as these in connection with other defensive measures is simply using a “belt and suspenders” approach. It’s a fine idea to consider adding to the mix, even if some people have better resources to draw upon.

  11. Many years ago when I was in an Army Reserves Infantry Co. I had come up with similar idea. They had wooden replicas of claymore mines, I rigged them up with a flash bulb and a 9 volt battery, and a clothes pin switch, they could aldo be rigged for command activation. Mede a good sileny alarm and ruind the night visio of the Scouts who were playing the role of OPFOR.

  12. Oh, How about a few stuffed
    Big man size (scarecrow like) stuffed pants and coat weighted dummy’s on pulleys and a downward slope laundry lines that are released via perimeter trip lines that charge/slide down toward the perimeter and slam face first into the tree the laundry line are attached to… It may draw some fire or the aggressor might laugh out loud…by that time, I have already started to flank his position…
    So, Come on’ lets play ! I ‘ll add Your gear to the collection….


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