To cheat at slots using a magnet, you could spin the reels and then use a strong magnet on the outside of the machine to stop them spinning when you saw your winning combination. Cheaters would then remove the magnet and claim the payout.

One common method is the use of optical sensors to scan the bill for specific security features, such as watermarks, security threads, and color-shifting inks. The machines may also use magnetic and infrared sensors to detect the magnetic properties and infrared marks present on legitimate currency.

Online games use random number generators (RNGs) to ensure their odds match the payout of land-based casinos. Mathematical analysis should indicate the payout will average over time.

In an electronic roulette, the ball landing on a specific number is determined by a random number generator (RNG) that is programmed into the game's software. The RNG uses complex algorithms to generate random and unpredictable outcomes, ensuring that the result of each spin is truly random.