SAN JOSE, Calif. (AP) - Colleges around the country are buying millions of coasters that test for "date-rape" drugs in drinks. But some experts say the coasters are ineffective and could lead to more assaults by creating a false sense of security.

The manufacturers - who also make fake snow and party foam - say the 40-cent paper coasters are 95 percent accurate. The coasters have test spots that are supposed to turn dark blue in about 30 seconds if a splash of alcohol contains drugs often used to incapacitate victims.

In tests at the Michigan State Police Crime Lab, however, the coasters failed to react clearly to drinks spiked with gamma hydroxybutyrate, a major date-rape drug known as GHB, said forensic scientist Anne Gierlowski.

"We tested red wine, cola, whiskey and orange juice and because three out of the four have color already, it was very hard to decipher a color change," she said. "It's a nice idea, but it's probably a nicer idea for the people selling them because they've probably made a lot of money."

Plantation, Fla.-based Drink Safe Technologies Inc. has sold about 50 million of the coasters since March, mostly to colleges and convenience stores, said president Francisco Guerra.

Guerra likens the coasters to condoms: While not 100 percent safe and effective, they are a good prevention tool.

"I've had 100 people say this saved them from getting raped," said Guerra, a former magician. "Before me, there was no way to detect it. It's nice to be able to do something about it."

A federal task force recently estimated that college drinking leads to an estimated 70,000 sexual assaults or rapes annually.

Yasmine Timberlake, a sophomore at San Jose State University, was grateful for the coasters handed out by the YWCA at a bar near campus.