Many drivers have a Fast Lane pass. They zip through tolls without having to dig for change. Drivers love the convenience, but it could get some in trouble.

During rush hour, normal tolls get congested. Drivers clumsily fumble for their change, but not Fast Lane holders. They can fly right through. But everytime they drive by, they give some information away. The plastic transponders attached to the windshield track the drive, down to the second.

It helps many private investigators, like Mark Chauppetta, president of On the Mark. He says there's a lot to be gained from these plastic devices.

"It's taking a snap shot of your vehicle, I believe it takes a snapshot of your license plate number. I'm not sure if takes a snapshot of the person in the car, so that's information that can be tracked," he says.

Chauppetta's in the business of getting the lowdown on spouse's personal lives

"They're snooping and trying to find someone cheating, someone being unfaithful," he says.

He says the Fast Lane statements mailed to your home, can be useful in doing just that.

'Why are you exiting this toll at 10 o'clock at night when you're supposed to be here,' are just some of the questions spouses ask," Chauppetta says.

The proof is in the transponder. Many times a cheater can get caught by taking the high tech route over paying out of pocket.

"It gives them a little bit of leverage if you go into court trying to divide assets," Chauppetta adds.

But it's not that simple. Divorce attorneys subpoena the Massachusetts Turnpike Authority for the records, but they're not always successful.

"It's something that can help an investigator, but only if we can get that information. Right now, it's almost impossible to get the information unless a judge signs off on it," the private investigator says.

The MTA says the records will remain sealed unless they have a court order. But you don't have to go through all that trouble in other states, New York and New Hampshire, included. Those records are open and used quite often as evidence in divorce court.