Ideas for a DIY remote alarm from car to house.

Our cars are broken into about once a year, or so it seems. I usually - but not always - remember to set the alarm on my truck with the remote on the key, but my wife’s car doesn’t even have an alarm. We learned long ago to never leave anything of value in the car, so these break-ins are more of an annoyance than anything.

What I would like to build (or buy) is something that I could connect to the dome light circuitry on my wife’s car that would remotely turn on a bright light in our bedroom. I don’t want a blaring alarm to scare the guy off. I want to be notified so I can call 911 before he gets too far.

So the basic idea is that when the car door is opened, the dome light will come on as usual, but also something like a garage door remote control is triggered that will activate a circuit inside the house that will, in turn, turn on a light in the bedroom.

I haven’t been able to find any off-the-shelf products to do this, so I’m looking at a DIY version.

Any help from the Dopers is appreciated.

Find a cheap transmitter and receiver, I’m thinking maybe the kind designed to turn a ceiling fan on and off. It’s increasingly hard to find, but you wouldn’t want one that requires wifi for this project.

Wire the receiver to a light in your house and the transmitter to the car. You’d pull the guts of it out (or not, if you have the space), find a way to make sure the button to turn the lights on is always pushed, and then wire it to the light.
The tricky part, I think, is going to be knocking the voltage down from 12 to whatever the transmitter is expecting, probably 1.5 or 3v. I assume that can be done with some resistors.

If you need more space, you could probably wire it to one of the door switches, or even a DRL if they come on when the door is opened.
Take a look at motorcycle forums, that’s where I got the idea from. A common thing to do is wire a garage door opener to your high beams. Then as you get near your house you can flash the high beams, which activates the garage door remote and (hopefully) your door is open by the time you get there.

A lot of sensors and switches work with wireless control hubs such as Samsung’s Smart Things. They aren’t completely bug free but it’s something to consider.

What is the distance between car and bedroom?

This might work and the price is right.

The tricky part will be to get the domelight to trigger the button. You’d also have to configure the reciever for interlocked mode (see the datasheet in the link) to latch the output relay to stay on for the indoor alert.

I’ve got a couple of these remote electric outlet controls so I can use a remote to turn things that are hard to reach on and off.

Should be easy enough to pull the guts out of the remote and connect it to the dome light

Are you handy with basic electronics (can you use a multimeter and a soldering iron)?

If you found one, there’s probably a million more. I didn’t look at the spec sheet, but the picture says 12vdc. You’d have to use it, with 12v source to power another 120vac relay…or use a light that works with 12v. Something driven by USB(5v) attached to that via a car charger would probably work.

I’ve been trying to find something like that for myself. At work I have outdoor lights on a timer, but if I want to turn them on during the day, I have to walk out there, open the box and flip them on. I’ve been looking for an ethernet controlled switch or a non-wifi wireless switch (or relay, whatever) to take care of this.

I just don’t think wifi will get from the timer to the router very well, or at all.
Also, I just glanced at that page again. The transmitter uses a “12v camera battery”, if that’s really the case, it could be wired right in to the car and the button physically taped down.

Thanks for the input, everyone. To answer some of the questions here - I’m a pretty competent DIYer, I have a multimeter and solder. The bedroom is pretty far from the cars, but the garage isn’t. I can run wires from the receiver in the garage to the bedroom.

I wonder if a mechanical trigger would be simpler. Basically, I would attach a spring activated switch to the glove box (which is what they always check) which would then trigger the transmitter, etc.

I was just thinking about this the other day. If you’re comfortable with an Arduino, I’ll bet you could put something together that uses a photocell to send a wireless signal to a receiver inside. Put the whole thing in a place that will expose the photocell to the dome light.

Of course, your inside [the house] light would then also need a timer or something so that it doesn’t have power during daylight hours or it’s going to be on all day.

As for a mechanical switch, I can’t speak to getting the signal inside, but getting a momentary switch installing it in the glove compartment would be trivial…in fact, there’s already one in there, you could tie in to that.

If you are comfortable doing some programming, you can use the TTGO ESP-32 based LORA module.
They are available on Amazon and eBay.
The LORA transmitter will go at least 1/4 mile in an urban area.

I used a cheap wireless doorbell set from eBay to create a warning system that tells me when our washing machine is done. These won’t transmit as far, but it’s a simpler project.

Using the Arduino (or Raspberry pi zero) is what I thought of as well. It has the advantage of some logic so it could be situationally (time and location) aware as well as selectively turning a light on or off. I had one in my garage which would turn on a light (hooked to wemo) if the door were open (using simply the amount of light that entered through the garage door). I had some fun with it and if would flash the light off and then back on if it had been open from more than 15 minutes.

I repurposed the set up for some Xmas light effects and never put it back.

You might also have a look over at for ideas. If this then that is a community of people who are looking to maximize interoperability of the world. One drawback is that there was a 15 minute time delay for some of their triggers, but I haven’t kept up recently.

Well, here’s my solution so far. Home Depot carries a product called “Wireless Doorbell and Mail Reminder Kit”. It comes with a doorbell base, two wireless buttons, and a mailbox alert sensor. The mailbox sensor is designed to be mounted on a typical mailbox door in a vertical position so that when the door is opened, the sensor is rotated into a horizontal position and a tiny ball (I assume) rolls into place to make a connection and remotely trigger the inside unit. I just mounted it to my glovebox instead of a mailbox, so when the bad guy opens the glovebox - as they always do - it will alert us. The only problem with that is that the sensor triggers inconsistently. Maybe I got a bad unit.

I thought I’d be able to use the wireless buttons as well, but so far, that’s been a bust. The buttons are powered by a 12-volt battery, as is the car. I figured I’d just remove the battery, wire the button to the dome light, and clamp the actual button (contactor, or whatever) to its closed position. Brilliant. I thought. The problem is the button doesn’t activate that way. You can’t push the button and then apply power. It has to have power first. I don’t know if that is built into the circuitry or if that is just the nature of things, but I haven’t figured out a way to get around that yet.

As far as the inconstancy, try rotating the sensor from vertical to horizontal (just holding it in your hand) and see if you can replicate the problem. I have a sneaking suspicion that with it being mounted on the glove box door it’s not tilting far enough to the horizontal to trip the sensor.
If that’s the case, I’d experiment with putting it on the side wall of the glove compartment and installing it so that when the door is open it’s at, or close enough to horizontal to trip the sensor, but making sure that when the door is closed, it’s standing up enough that the sensor isn’t constantly being set off.

Does that make sense? I can picture it in my head, I just hope I’m explaining it clearly enough.

Get an auto horn from a wrecking yard or a very loud 12v siren and wire it to the glove box light.

And maybe put a switch on your dashboard to disable it when you’re in the car.

That’ll take 3 or 4 times before you remember not to do it in traffic.

Right. That’s what I’ve done. I haven’t actually mounted it yet but testing it by just rocking it back and forth yields inconsistent triggering.

That stuff is a little intimidating, but I’m beginning to be intrigued by it. Are there any “how to’s” for that?

I believe there’s roughly about 85,000 youtube videos on it, as well as books and DVD’s you can buy and websites dedicated to it.

Having said that, every time I’ve looked into getting one, I get overwhelmed with all that and skip it. I know about them, I have an idea as to what they can do, but I don’t know how they do it. I spent a few years coding in high school and college, but when I poke my head into these sites I remind myself that I don’t want to start coding again for fun.

From the OP:

I don’t want a blaring alarm to scare the guy off. I want to be notified so I can call 911 before he gets too far.