The Non-Electronic Bug

There couldn't be a better tip-off system than mine—it wasn't possible—but he had one!
I wouldn't take five cents off a legitimate man, but if they want to gamble that's another story.
What I am is a genius, and I give you a piece of advice: Do not ever play cards with a stranger. The stranger might be me. Where there are degenerate card players around, I sometimes get a call. Not dice—I don't have a machine to handle them. But with cards I have a machine to force the advantage.
The first thing is a little radio receiver, about the size of a pack of cigarettes. You don't hear any music. You feel it on your skin. The next thing is two dimes. You stick them onto you, anywhere you like. Some like to put them on their legs, some on their belly. Makes no difference, just so they're out of sight. Each dime has a wire soldered to it, and the wires are attached to the little receiver that goes in your pocket.
The other thing is the transmitter I carry around.
My partner was a fellow named Henry. He had an electronic surplus hardware business, but business wasn't good and he was looking for a little extra cash on the side. It turns out that the other little wholesalers in the loft building where he has his business are all card players, and no pikers, either. So Henry spread the word that he was available for a gin game—any time at all, but he would only play in his own place—he was expecting an important phone call and he didn't want to be away and maybe miss it.... It never came; but the card players did.
I was supposed to be his stock clerk. While Henry and the other fellow were working on the cards at one end of the room, I would be moving around the other—checking the stock, packing the stuff for shipment, arranging it on the shelves, sweeping the floor. I was a regular model worker, busy every second. I had to be. In order to see the man's hand I had to be nearby, but I had to keep moving so he wouldn't pay attention to me.
And every time I got a look at his hand, I pushed the little button on the transmitter in my pocket.