Paranoids take note: You aren't alone when you drop your money into a slot machine these days.

Increasingly sophisticated technology is allowing casinos to monitor individual slot-machine players even as they're feeding the beast with coins. A trade-journal ad for a system made by Las Vegas-based Casino Data Systems Inc. says it all: ``Mary Alice Grunwald just redeemed 1,000 Bonus Points, bought $100 in silver and right now is $27 ahead on Carousel 9 Video Poker Machine No. 1306. Anything else you need to know?''

So-called player-tracking systems have been around for some time, but until recently they were relatively primitive. The innovation is ``real time'' monitoring of a person's play, in effect giving the casino a tool to know exactly how much the player at each machine is winning or losing as it's happening.

For the casino, tracking players is a powerful marketing tool _ a way to figure out who spends the most time at slot machines and how to keep them happy.

Though there's still some social stigma attached to gambling, many slots players volunteer for such scrutiny, if somewhat unwittingly. They join the slots clubs that each casino pushes as a way to win free dinners, shows, clothes and other complimentary delights. The tracking begins as soon as a club member inserts a membership card into a slot machine to register for the points that allow them to redeem their gifts.

The cards enable the casino to keep a detailed history of each person's gambling and habits, including their favorite drink and whether they're drawn to 25-cent video poker games or dollar slot machines.

Between 30 percent and 70 percent of the slots players in a casino at any given time belong to a slots club, according to International Game Technology, a large casino-equipment manufacturer based in Reno, Nev. The figure is usually closer to 30 percent in a tourist casino and closer to 70 percent in a casino that caters to a local market, where players can gather club points more easily over time.

Even when gamblers don't join clubs, though, player-tracking systems are helping casinos hunt down the players they want to know more about. New ``cardless'' features of the systems flag casino managers if a machine is in hot-and-heavy play. When such usage is detected, the casino can send someone out to greet the gambler, offer him or her a drink and recommend slots-club membership.

It may all sound a bit Big Brotherish. But the casinos deny that any of the information they gather is given or sold to anyone else. And many heavy slots players don't seem to mind that casinos are accumulating dossiers on their gambling habits if providing the information guarantees red-carpet treatment.

Take the case of Dale Hall of Cleveland, who was camped at a bank of Harrah's slot machines in Las Vegas on a recent night. He, his sister and some friends are all avid slots players and belong to several Las Vegas slots programs. Player-tracking has clearly flagged Mr. Hall and his contingent as gamblers worth courting. They were recently deluged with offers from several Las Vegas casinos for complimentary rooms, meals and the like.

If their privacy is being invaded, they say, then by all means, invade it some more. ``They claim you're watched here most of the time anyway,'' shrugs Mr. Hall as he prepares to take a break and dash over to the Excalibur Hotel and Casino, where another free dinner awaits.

Down the street at the Flamingo Hilton, Renee Brocca of Los Angeles is equally unconcerned about using her Hilton slots club card while she gambles. ``I'm sure they keep track of how I'm using my Visa card, too,'' she says. ``What's the difference?''

``I don't think it's any different than when they award travel to a good Neiman Marcus customer,'' says David Thompson, chairman of Mikohn Gaming Corp., which manufactures a player-tracking system called Casino Link.

Some players do take exception, though. Because slot machines are easy to play _ and seemingly private _ they attract a lot of new gamblers who are intimidated by table games. ``For them to be able to track everything I do, it's like an invasion of privacy,'' says Faye Jaffer, a first-time Las Vegas visitor from Vancouver, British Columbia.

The information that's accumulated is most useful to casino managers, who are always looking for better ways to reel in high-volume gamblers, but it also helps the casino analyze which machines are popular, which is crucial when machines are arranged on the casino floor.

``We need to know what people want, what they don't want, what their tendencies are,'' says Peter Morton, chairman of Los Angeles-based Hard Rock Corp., which owns the Hard Rock Hotel and Casino in Las Vegas and uses a player-tracking system made by International Game Technology. The information is especially critical at the Hard Rock, which with just 345 rooms is much smaller than its Las Vegas competitors and has to put on a more personal face for its customers.

So far, slot-machine play is the only type of casino gambling that is eligible for player tracking. Table games are monitored with video cameras for security purposes, but to date it has been impossible to precisely calculate how much a player is spending at craps, blackjack or roulette. The play moves too fast and the games aren't computerized, as slot machines are.

That may be about to change, though. Mikohn is about to begin testing a system that will place small computer chips inside the poker chips that players use to bet. A scanner slipped under the felt of a blackjack table will be able to read the chips, making a precise record of how much each player is wagering.

The system will also make it practical for casinos to offer club memberships to table-game players. That means the casinos will eventually be able to monitor players by name.