By Natasha Baker

TORONTO (Reuters) - Before getting behind the wheel after a night out, a driver can test his blood alcohol level with new apps that not only give a reading but can call a cab.

Breathometer, for iPhones and Android smartphones, and BACtrack, for iPhones, display a user's blood alcohol level within seconds on smartphone-connected breathalyzers.

"People think, 'Oh, I'm driving around the corner,' but it's not until they get pulled over that they realize they're over the limit," said Charles Michael Yim, chief executive of Breathometer, based in Burlingame, California.

More than 1.2 million people were arrested in the United States in 2011 for driving under the influence of alcohol, according to Federal Bureau of Investigation data.

Yim said his company's aim is to prevent drunk driving by raising awareness of alcohol levels and enabling drivers to make smarter decisions.

The Breathometer plugs into a smartphone's headphone jack, and the user blows on the device. The BACtrack connects to the iPhone via Bluetooth. Both use sensors that meet U.S. Food and Drug Administration standards and can detect blood alcohol levels with accuracy within 0.01 percent, according to the companies.

Breathalyzers have been around since the 1950s. By pairing them with smartphones and making them smaller and more cost effective, more people will be able to use them, Yim said.

"We are catering to a completely different audience that wouldn't have considered buying one before," he said.

Breathometer's breathalyzer is the size of a car key and fits into a pocket or on a key chain. The app can detect a user's GPS location, order a cab if the user can't drive home, and estimate how long it will take for the user to become sober.

"Just checking blood alcohol levels can help you be more aware of your body. If you blow 0.02 percent or 0.04 percent you might think, 'I better stop drinking,'" Yim said.

In all 50 U.S. states, a blood alcohol level above 0.08 percent is considered drunk driving. The National Transportation Safety Board is recommending the limit be reduced to 0.05 percent. More than 10,000 people died in drunk driving accidents in the United States in 2010, according to the National Highway Traffic Safety Administration.

The Breathometer app reads signals after the user has blown into the breathalyzer. An ethanol sensor embedded in the device detects alcohol on the breath and converts this into a signal, which the app processes.

The app, which costs $49, will be released worldwide in October on the Internet and in stores the following month.

San Francisco-based BACtrack, founded in 2001, was the first company to receive U.S. government clearance to sell breathalyzers for personal use. Its breathalyzer, which includes a mouthpiece, costs $150.

The app also tracks a user's drinking habits in a graph, and can estimate when a user's blood alcohol level will return to zero. Users can also share their blood alcohol levels through text message, Facebook or Twitter.

"It's not about whether you're at 0.05 or 0.08 percent. If you even have 0.01 percent you should not be driving," said Yim.

(Editing by Patricia Reaney; Editing by John Wallace)