Ah. Damn.
I think I mentioned in my first / introductory post here on this forum that I am an enthusiast (as in, not a professional or regular electronics student). As such, electronics projects are purely for hobby and diy for me.
Yes, I know I can simply use a digital number lock on the cupboard and tell the combination to my wife.
I could also just order a SONOFF and get a WiFi device. While way overpriced, it's definitely in the budget.
Or I could just get a $25 ringtone detector from eBay. I saw the custom built circuit from some Romanian guy.
Then why do I keep asking for doable (as in, which I can develop myself) methods when I can just buy a ready-made solution easily, both online and offline? Simply because electronics is my new hobby and it gives me a sense of accomplishment and pure joy to develop something in this field or put together different parts to build something which accomplishes a meaningful task.
And yes, I know IEDs have been detonated through the same method since decades.
Which leads to the point that if I had bad intentions, I would just get the ringtone detector and use it to ignite the primer. Duh, why go 2 extra miles, make an account on an electronics forum and ask and argue for nearly two weeks?
P.S. I haven't posted any update on the project because I live in a rural area and I'd have to travel to the town to get the required parts. Heck, even if I order online, it would get delivered it in the town and I'd to collect it from there.