How to make a tiny spy transmitter

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Surface mount electronic components are not very hobbyist friendly. It is a shame but nobody will ever build the next iPhone in their garage again. Likewise the image of the spy with soldering gun is getting replaced with the spy and a laptop surfing shopping sites.

How big were audio bugs in, day, the 60s and 70s, and what were the specs compared to now?

It’s funny, I was just thinking about spycraft bugs yesterday. Are you BUGGING MY BRAIN, bb?!

Current shenanigans demonstrate that the ‘de rigueur femme-fatale sitting on face while being filmed in hotel room’ is still part of spy-craft.

No, just your phone.

No wonder Trump couldn’t find these little buggers in his office !

There was a book in the sixties about bugging, by a well known ham radio operator. The publisher aimed towards electronic hobbyists, so I don’t know what the intended market. I don’t have it handy, but memory sys it started as a magazine article.

It was in effect a survey at the time, and some of it was off the shelf. Go into Lafayette Radio or Radio Shack, buy something and put a new badge on it. But that included bug detectors.

Infinity bugs were great, since they were installed in phones (so they didn’t have to be very small) and got power from the phone line. But also, they worked by someone phoning that phone, it turned on before the phone rang, and then someone could remotely listen to any conversation in the room.

Early bugging predates transistors, so either they ran wires to somewhere that a listener can be stationed. Or tube transmitters, hidden in place like walls. Phone taps meant access to the phone wires.

Transmitting bugs often were rudimentary, so they could be small, though performance wasn’t great. The trick was to run them on a frequency where few had receivers, so retuning to adjacent to the FM broadcast band was a scenario.

Electret capsules aren’t “small” but before they were common microphones were “big”. But even in the sixties the bugs could be “small”, button cells and tiny transistors, one trick was to grind off some of the plastic casing to make them smaller. Use a higher frequency to keep the coil(s) small.

You have to think through the scenario first. Too small and the battery my die after a few days. You can’t even put a bug in a tv set or radio these days, no longer is there empty space in those. But then some tv sets now have microphones, thus the potential for someone to listen in, and the same for computers, especially laptops. But however simple it looks on tv, it probably isn’t so easy.


I built a couple of simple FM radio transmitters in the 1980s. They just used a single transistor, a cap and an inductor made by winding stiff wire around a pencil. One day I put one in my sisters room when my mother was reading her a book. I got into my car, turned the radio on and started driving. I got a kilometer away. The signal was still strong, and I decided to rush back and switch it off.


That there is a great post, thank you for that info!

I think I still have a book on building bugs from the early 1980ies or so somewhere. Never got around to build one though. Stuff like that was always popular with the DIY electronics/radio ham crowd. Usually just to see if it works, not to really stalk anyone, as far as I can tell. Also, at that time, the post office still had detector vans cruising the streets.

Today? To bug any office, hack the phone that’s already on the desk.
This got really easy with ISDN some 25 years ago. All the telephone exchange system had options for remote maintenance and, then as now, a lot of people don’t change the default passwords/codes.
Current VOIP systems can’t be that different.

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Well, it was in the 70s that the “martini olive” bug became well known. The circuit would likely have been pretty similar to this one. Although I think there has been some progress in acoustics to allow them to make microphones that small.

The part that surprises me is the receiver: he’s using a software-defined radio that costs only $27! Sometime 5-10 years ago, I went looking for a cheap SDR and couldn’t find anything under about $400. I’m going to have to get one of those!

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Those cheap DVB-T dongles (which are easily repurposed as SDR receivers) are awesome. I have one of those listening to my 433 MHz temperature/humidity sensors, so I can graph their readings.

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There is only one problem with this project in the US: it is illegal to transmit audio continuous in the 433MHz band. It’s meant for short duration remote control type applications.

In the US, it’s part of the amateur radio 70-cm band. It’s not for remotes, although 433 is used for that in some other countries.

The device would be legal if you had an amateur license and gave your call sign periodically. And not many hams would get upset about such a low power transmitter operating in their bands. Most that I know would say, “hey, come to our meetings; our hobby is dying out!”

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