Most slot machines in land-based casinos still use a sensor to determine how many coins or bills are being inserted. By interrupting these sensors with a pocket laser light you can make the machine think you're inserting coins or bills while you aren't.
No, there is no way to predict when a slot machine is going to hit a jackpot or to determine which machine is going to be lucky. Slot machines are programmed to use a random number generator (RNG) to determine the outcome of each spin, and the RNG generates random and unpredictable results.