The repairman
Carmichael ran a television repair shop in Tulsa, Oklahoma, when a friend showed him a device in 1980: the top-bottom joint, a length of guitar wire and a bent metal rod. Pushed into the coin slot and the payout chute of an electromechanical slot machine at the same time, it closed a circuit the machine expected only when it was paying a win, and the hopper obliged. He drove to Las Vegas with it and, by his own later account, cleared a few hundred dollars from a machine in a bar on his first try.
The joint worked because the machines of that era were built like the machines they had evolved from: relays, switches and a motor, in which “a win has occurred” and “the hopper should pay” were the same electrical event. Fake the event and you had the payout. Carmichael was arrested in 1985 with the device in his possession, served part of a five-year sentence, and came out into a different casino floor.
Three tools, one gap
By the late 1980s the electromechanical machines were gone, replaced by video and computerised slots that decided each spin with a random number generator and used the hopper only to pay. The joint was useless against them. Carmichael did what a repairman does: he bought a machine, took it apart at his bench, and looked for the seam between the decision and the delivery.
| DEVICE | YEARS | WHAT IT DID | WHAT IT FOOLED |
|---|---|---|---|
| Top-bottom joint | c. 1980–1985 | A rod and a wire inserted at both ends closed the payout circuit | The relay logic of an electromechanical machine |
| Monkey paw | late 1980s | A bent rod fed up the payout chute tripped the coin-counting switch | The mechanical switch that counted coins leaving the hopper |
| Light wand | 1990s | A small bulb on a camera battery, slipped into the payout slot, blinded the optical coin sensor | The optical sensor that told the computer how many coins had been paid |
In each case the game’s decision was untouched. What was attacked was the machine’s knowledge of its own payout.
The light wand was the elegant one. A modern machine of the time decided a spin correctly, decided the payout correctly, and then instructed the hopper to release that many coins while an optical sensor counted them out. Blind the sensor and the count never reached its target, so the hopper kept releasing coins into a waiting hand. The computer was not wrong about anything. It had simply been made unable to see.
Carmichael and a small crew worked machines across Nevada, and by some accounts as far as Atlantic City and the Caribbean, through the first half of the 1990s. He was arrested in Las Vegas in 1996, and again later, and in 2001 pleaded guilty to federal charges connected to the devices; he served a short sentence and probation, and in 2003 the Nevada Gaming Commission added him to its List of Excluded Persons, the Black Book, which bars a person from entering any casino in the state.
The machine knew who had won. It did not know what it had paid.the whole career, in two sentences
Decision and delivery
It is worth separating what Carmichael did from what Ronald Harris did a few years later, because the two are often filed together as “slot cheats” and they attacked opposite ends of the machine. Harris, a state engineer, altered the decision: he put code into the machine that made it produce a jackpot on demand. Carmichael never touched the decision. He let the machine decide honestly and lied to it about the delivery. A machine can be secured against one and still be open to the other, and the industry’s answer to Carmichael was not a better random number generator but a better sensor, and then the removal of coins altogether in favour of printed tickets.
That is the design lesson, and it applies directly to a game with no hopper. On this site the delivery is not a physical act that a sensor watches. When a round settles, the payout is the stake multiplied by the result’s multiplier, rounded down to cents, and credited to the balance. There is no coin to count, no chute to reach into, no optical gate to blind. The number that is paid is the number that was decided, because it is the same number.
- A physical machine has two truths: what it decided and what it delivered. Carmichael lived in the gap between them.
- A hashed game has one. The decision is a function of the seed, the payout is a multiplication of the decision, and the verifier checks the first, which fixes the second.
- The remaining attack surface is the decision itself, which is why the seed is committed before play and revealed after. That is Harris’s end of the machine, and the commitment article is about closing it.
Who was Tommy Glenn Carmichael?
A Tulsa television repairman who cheated slot machines from about 1980 to 1996 with home-made devices: the top-bottom joint, the monkey paw and the light wand. He was imprisoned in 1985, arrested again in 1996, pleaded guilty in 2001 and was added to Nevada’s Black Book in 2003.
How did the light wand work?
A small bulb on a camera battery, slipped into the payout slot, blinded the optical sensor that counted coins leaving the hopper. The machine had decided a payout correctly but could no longer see how much it had paid, so the hopper kept paying.
How is that different from the Ronald Harris case?
Harris altered the decision by putting code into machines that produced jackpots on demand. Carmichael left the decision alone and fooled the delivery. They attacked opposite ends of the machine.
Why does this not apply to an online game?
Because there is no delivery to fool. The payout here is the stake times the result’s multiplier, rounded to cents and credited directly; the result is a function of a committed seed. Decision and payout are one computation with no sensor between them.
What is the Black Book?
Nevada’s List of Excluded Persons. A person on it may not enter any casino in the state, and a casino that admits them can be penalised.
- Nevada Gaming Commission — List of Excluded Persons (Carmichael added 2003)
- Contemporary reporting on the 1996 Las Vegas arrest and the 2001 federal plea (Las Vegas Review-Journal, Las Vegas Sun)
- Wikipedia — Tommy Glenn Carmichael: devices, arrests and later life
- Betkyo engine source: _shared/demoLocal.ts (centsFloor settlements), the per-game derive modules
