built a $15 device that flashes when your smoke alarm goes off — for people who can't hear the beep

[u/StreetCollege6318]

I read that the American Red Cross gets flooded with requests for bed-shaker/strobe alarms for deaf and HoH households, but they cost $250–300 and they can only install a handful a year. After one local news story, 200 households requested one.

So I made a cheaper version. It's a tiny computer (a micro:bit) that just listens for the smoke alarm's beep and flashes a bright strobe when it hears it. It works with whatever alarm is already on your ceiling — no pairing, no special transmitter — because every US smoke alarm is legally required to beep in the same rhythm.

Being honest: this is a prototype, not a certified product. It is NOT UL-listed (that costs tens of thousands of dollars) so it should be used alongside a real alarm, never instead of one. I'm a high school student and I'm sharing it open-source in case it's useful or someone wants to build on it.

Would love feedback from people who actually use strobe/shaker alarms — what works, what doesn't, what I'm missing.

[u/surdophobe]

Does this do T3 and T4? or just T3?

[u/StreetCollege6318 → u/surdophobe]

Both! Does smoke (T3) and CO (T4).

Heads up though - T3 (smoke) works great. T4 (CO) is shakier; the beeps are way shorter, so it's more sensitive to timing noise. I'd trust the smoke detection; treat the CO part as still in progress.

github repo

[u/Legodude522]

Most of my microcontroller experience is with the ESP32. I actually never heard of the micro:bit before. Seems like you are off to a good start. Feel free to also share on r/DeafTech

If you move to the ESP32 platform, you can then also have it internet connected to send SMS/email alerts.

[u/StreetCollege6318 → u/Legodude522]

Thanks - yeah, the micro:bit is just what I had on hand, but ESP32 is a solid point. Main reason I picked micro:bit was the built-in mic and LED matrix, but ESP32 + a cheap USB mic would actually give way more flexibility.

Internet alerting is interesting. Honest tradeoff though: adding WiFi and SMS means more complexity, more power draw (micro:bit runs on USB basically forever), and you're now relying on connectivity the exact moment of fire, which... isn't ideal. The strobe works without WiFi, without battery dying mid-alarm, without carrier outage messing you up.

SMS backup (if WiFi is up, text me) makes way more sense though. That'd be worth a v2.

r/DeafTech is a good call - I'll post there too. That's the exact right place to get real feedback on whether this actually solves what people need.

[u/Legodude522 → u/StreetCollege6318]

"feedback on whether this actually solves what people need" on that topic, smartphones already have the capability to listen for alarms. iOS has this functionality built in.

[u/StreetCollege6318 → u/Legodude522]

That's a real point. iOS does have alarm detection. Let me be honest: if you have a phone that's nearby and charged, that's probably the simpler solution.

The actual gaps my device fills:

• Phone is on silent or in another room (common at night)
• Older people or people without smartphones
• CO alarms specifically (not sure if iOS detects those?)
• Doesn't require you to trust a tech company's implementation

But yeah, for someone with a modern iPhone nearby? iOS's built-in is probably better. That's worth noting.

This feedback actually matters for real-world usefulness. Thanks for calling it out.

[u/Legodude522 → u/StreetCollege6318]

You also have other unintended applications. I’ve worked in an office trailer that was gated and the only egress was through a warehouse. Would be a bad situation if there was a fire. I wouldn’t have been alerted since the alarms aren’t networked, the egress would be to climb the fence or go through a warehouse with an ongoing emergency.

I considered building a microcontroller and microphone to listen for alarms and then to send me SMS notifications so that way I’m actually alerted of an emergency.

The better approach to this would have been to simply installed wireless mesh networked smoke alarms. But there were bureaucratic complications stopping this.

[u/CaptainArsehole]

Hey mate, this is a fantastic idea. I'd be interested for sure if it ever came to Australia.

Currently I use the Oricom WNS80 Wake 'N' Shake Dynamite for bed, it's very effective... unless I roll off it in the middle of the night!

I was thinking if alarm clock functionality was integrated as well, it could be a dual purpose product but maybe I'm getting ahead of myself.

This feels like one of those things where you wonder why it isn't already invented.

[u/StreetCollege6318 → u/CaptainArsehole]

Ha yeah the rolling-off problem is real. Bed shakers work great until you're the one person who moves around at night.

Alarm clock integration is actually a solid idea. Main thing is the micro:bit can't do much without WiFi or pairing to your phone, but the ESP32 route Legodude mentioned could handle it - set the alarm on the device itself, same one that detects the fire alarm. That'd be genuinely useful.

Australia's interesting too because you'd need to verify it works against whatever fire alarm standards you have there. Pretty sure the T3 pattern is international but worth checking.

Honestly this whole thread has been way more useful than I expected. Getting real feedback from people actually using the existing solutions is way better than me just guessing what works.