With the draconian penalties that currency forgers can face, there are plenty of disincentives for trying to pass fake dollars anywhere; with all the surveillance equipment at their disposal, casinos are certainly among the more risky places to attempt it. But people still try, and with the volume of notes that passes hands here every day, undoubtedly some get away with it. But most get caught.
For example, while researching this answer, we came across a Department of Justice press release relating to one Sean Daker, who pled guilty to passing the grand sum of $60 at the Jackpot Casino in Billings, Montana. Although eventually sentenced to only 28 months in jail and a restitution payment of under $3,000, Daker faced possible penalties of a 20-year sentence and $250,000 fine.
Last Christmas, law enforcement in Las Vegas and Mexico broke up a ring that had been passing counterfeit $100s in California, Arizona, and Nevada. Their technique involved bleaching $5 bills and changing them to look like $100s, but the Secret Service, which was called in to investigate the case (fake money falls under their remit), demonstrated to reporters how the five-dollar bill could be easily detected by its distinctive blue glow under ultraviolet light. As one agent put it at the time, "If you want to remember the color of the $100, $50, and $20 glow, just think of a traffic light. Red is on top, yellow in the middle, and green on the bottom." He estimated that $10,000-$30,000 a week in fake bills is passed in Las Vegas, which spikes to $40-$50K on a holiday week, but in relative terms that's still a drop in the ocean, and less than ½ of one percent of all American currency in circulation worldwide is thought to be counterfeit.
As far as slot machines go, the bill validators (which often spit out perfectly legal tender, just because it's a bit too crumpled, or even for no obvious reason at all) pretty much eliminate any risk of casinos getting hit by dodgy notes in the machines. Similarly, more and more casinos are adopting RFID technology in their chips. Although this is aimed primarily at being able to track each person's play, an added bonus is that this technology also renders the chips essentially unfakeable.
The drop boxes on table games don't yet contain the same kind of bill-valdiating technology as slots and thus are more vulnerable, although a contact at the Gaming Control Board informed us that the casinos are developing technology that will also validate bills at the table. In a past life making documentaries, this writer recalls filming in the surveillance room at a major off-Strip casino over a busy holiday weekend, when a couple tried to pass off some fake $100s. They got away with it on a blackjack table with an inexperienced dealer, but were caught on camera both there and at the cage, and were later picked up at a different casino (most properties are hooked into a communal and global computer database and share information with each other about cheats and scammers).
The $100 bill has long been the most counterfeited note on the planet and thus is subject to close scrutiny, so as far as domestically-forged bills are concerned, it's generally the lower denomination notes -- $5s and $10s mainly –- that people attempt. Counterfeiting U.S. currency, in particular the $100, has been a tactic of certain overseas terrorist groups in recent years, however, aimed both at destabilizing the Western economy and increasing their purchasing power in foreign markets.
While Hezbollah has been known to be operating illegal printing presses since the mid-'90s, producing passports and fake $100 bills, the only hundred-dollar bill that really scares the authorities is the so-called "super note," which is thought to originate in Syria, Iran, and North Korea. This is printed on authentic rag cotton paper using the same sophisticated intaglio machines used by the U.S. Mint, and is so close to perfect that it's virtually undetectable, although not with advanced technology, but we’re assured that its appearances in Las Vegas are rare.
