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Getty ImagesTrue, the machines used by law-enforcement officials to gauge your blood-alcohol content (BAC) are far more accurate than the Breathalyzers you can buy off the Internet. But buying one of these gadgets to use after you drink and before you drive isnt a bad idea—especially since inexpensive Breathalyzers can actually overestimate your BAC, meaning youre more likely to get a ride home if youve had alcohol instead of getting behind the wheel.

Some tips to remember before trying this at home:

• Always wait at least 20 minutes after drinking to use your Breathalyzer. The gadget measures the alcohol level in your breath; any residual alcohol in your mouth may interfere with that reading.

• Read the instructions on your Breathalyzer carefully before using it to ensure best results. For most models, youll breathe deeply into the mouthpiece for five seconds to get a reading.

• Know that even if your BAC registers below the legal limit of .08, your ability to drive may still be significantly impaired. So when in doubt, wait before you get behind the wheel, or have someone else (whether its a friend or a cab) drive you home.