Remember those scenes from 21, Ocean’s Eleven, and any film about cheating at or stealing from a casino? The ones in which a security team is trying to track the crooks’ activities across the floor using camera feeds?

It turns out casinos aren’t relying as much on not-so-secret surveillance to collect information about you as you might think.

If you’re gambling, you’re giving it to them voluntarily.

Casino rewards programs and loyalty cards, like MGM Resorts International’s M Life and Caesars Entertainment’s Total Rewards, allow casinos to track your habits and capture your preferences so they can entice you to play for longer and come back more often. They give the casino information about everything from what you play, to how often, to how much you spend and what kinds of food and beverages you purchase.

Here’s how it works: Loyalty program participants swipe player cards at machines and tables instead of wagering with bills, coins, or tickets. These cards let casino hosts know exactly where you are, how much you’re betting (and losing), and even how quickly you press slot machine buttons. And because they are linked to your preferences, a host may appear with a gin and tonic—or your beverage of choice—when it looks like you’re winding down for the day.

To incentivize customers to sign up for and stick with their rewards programs, casinos offer free and discounted nights at hotels; complimentary drinks, meals, and valet parking; and points for spending money that can then be redeemed for onsite discounts, cash, and more. These perks make gambling, and gambling for longer and with more money, even more appealing.

In fact, some gamblers have sued casinos, saying that the incentives fueled their gambling addictions by making it impossible to leave—and in turn, prompted them to lose millions of dollars.

And since many casinos are franchises under just a few large corporations—Caesars has multiple locations of the same name and also owns Harrah’s, Horseshoe, Bally’s, and more—your rewards program information travels with you across the country and around the world.

According to Ron Schlecht, founder and managing partner of BTB Security, most loyalty programs aren’t storing highly sensitive, personal identifying information that could be compromised in a hack or leak. While it’s possible that your loyalty account could be connected to a credit card number, most of the data collected is used merely to market to customers and keep them happy (and happily spending money).

Of course, casinos still use surveillance cameras for safety and security purposes: to look for players who may be cheating and employees who are tipping them off (or straight-up stealing), says Schlecht. And some machines have built-in cameras, so even players who aren’t participating in a rewards program may have their movements recorded.

But when it comes to tracking individuals habits, loyalty card swipes provide the majority of the insight to casino hosts who want to keep players playing.