JOHNSTOWN, Pa. -- Brian Thomas and Lauren Sonkin met us at Tulene's South Side Saloon in Johnstown to put the BacTrac Personal Breathalyzer to the test.

We asked them how they know when to stop drinking.

Thomas said, "I just drink until I feel like I reached my limit, then I stop." Sonkin said, "I just basically feel it out. If I feel like I'm losing control of myself or I'm not thinking straight, then I've probably had too much to drive."

Both also travel in groups of friends that have a designated driver or call a cab. They agreed the BacTrac personal Breathalyzer would be very useful.

Sgt. John Herdman of the Richland Police Department helped administer the test.

"We give a series of field sobriety tests. The last test we give is the breathalyzer and we use that as a pass-fail type thing."

Both Breathalyzers work the same way, but the personal one doesn't have a mouthpiece.

Sonkin drank two cranberry and vodkas over an hour and a half. Thomas drank three beers in an hour. With the personal Breathalyzer Sonkin blew a 0.02 percent and Thomas blew a 0.11. The legal limit in Pennsylvania is 0.08.

Herdman had Thomas and Sonkin blow into his police-issued Breathalyzer. Sonkin blew a 0.03.

"That's pretty close," Herdman said.

It was Thomas' turn; he blew a 0.045.

"That's a big difference, " Herdman said.

Brian used the personal Breathalyzer again and blew a more accurate reading of 0.07.

"Any type of personal breathalyzer you use is going to be a different reading than an actual Breathalyzer or blood test," Herdman said. "If you see that you're over the limit are you going to say, 'Hey, I need to get somebody to drive me home,' or are you going to say, 'Well, they might be wrong. I'm going to drive anyhow."