I live on the 4th floor of a low-rise condo building with a concrete parkade beneath. We have a serious problem with bicycle theft -- someone is coming in late at night with an angle grinder, and cutting through the locks securing the bikes to the installed racks like they were warm butter. I want to quickly build an ad-hoc alarm system using a microphone and some vibration sensors/accelerometers, and have made a prototype using an arduino, powered by a LiPo pack. It seems to work pretty well in identifying a theft-in-progress situation, based on noise and vibration. My question: is there a wireless transmission solution (that is legal) that I could use to transmit a signal from the alarm to my unit up on the 4th floor? There isn't any wiring or other physical infrastructure I could use for this, and nobody's wifi penetrates to that area of the parkade sufficiently. I thought about setting it up with a cellular phone radio, but the signal strength isn't great in that corner of the parkade, and I'd rather avoid the overhead and expense of that solution if possible. Does anyone know of any other wireless transmission solution that would work? The signal would have to make it out of an underground concrete parkade, then up through 3 floors of (mainly wood) condo material, but it would be extremely low bandwidth -- basically just "I'm going off! Come check the bike racks!"
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\$\begingroup\$ Assuming you get a radio that works, what happens next with you being on the fourth floor and the villain on your bike riding away rapidly? Wouldn't triggering a camera be better in terms being able to recognize the villain and reporting stuff to the cops? They seem to work nicely with tigers and other animals in their habitat. Even camera warning notices might be somewhat useful. \$\endgroup\$– Andy akaCommented Jul 9, 2023 at 15:38
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\$\begingroup\$ If parking has WiFi, you can use it to send signal. Peer to peer looks impossible. \$\endgroup\$– user263983Commented Jul 9, 2023 at 16:39
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\$\begingroup\$ Thanks for the comments and ideas. Yes, I do agree with you about the specific utility being somewhat questionable, but as soon as I'd had the idea, I wanted to know if it could be done! Ideally the signal to me up on the 4th floor wouldn't be to try catch the thief, but to reset all the beeping and flashing and sirens that would have caused them to turn and run immediately. =) \$\endgroup\$– MattCommented Jul 10, 2023 at 2:33
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\$\begingroup\$ When I bought a bicycle lock I checked consumer advise for these and basically they say that no lock will endure an angle grinder in the long run. The difference between locks is how long it will take to saw through them. If you look at premium locks/chains like the ones used for MC, they can resist angle grinder torture for many minutes and angle grinders are noisy. So there's a good chance that the thief will get nervous or wake half the building if the lock is tough to crack. Might be worth looking into before anything else. \$\endgroup\$– LundinCommented Aug 10, 2023 at 6:59
1 Answer
Let's put aside the wisdom of being awakened at 3 a.m. by an alarm, running downstairs and confronting a bike thief in your PJ's, and focus on technology.
The concrete-walled and -roofed parkade is a serious obstacle to microwave signals, including WiFi and modern cellular bands. You might be able to use LoRa (800-900 MHz in US and Europe); because of its narrow bandwidth it can tolerate greater propagation loss. You could run a cable from your sensor to a LoRa module mounted on the exterior wall of the parkade. The monopole antenna should stick out perpendicular to the wall.
If there are electrical outlets in the parkade, you could just extend WiFi coverage to the parkade. You'll need two "powerline WiFi extender" units, one in the building with a WiFi connection, and the other plugged into an outlet in the parkade. Then just add WiFi to your alarm sensor.
Having suggested these, I agree with commenters that a security camera system is more likely to safely document the theft and perhaps identify the thief.
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\$\begingroup\$ I hadn't thought of the powerline route. That's a very good idea and I bet it'll work. I will try the LoRa anyway, because I'm really curious and haven't dabbled with it before. \$\endgroup\$– MattCommented Jul 10, 2023 at 2:35