Even conscientious people make mistakes when they've been drinking, especially when it comes to knowing if they are impaired. You may have no intention of driving drunk, but drinking at all tends to make you overestimate your abilities. If you do not have a designated driver with you, you need to determine if you've had too much to drive safely.
If you are with someone who is not drinking, they can give you a sober assessment of your condition. Although this method is not scientific, someone who is not drinking has a better understanding of your condition than you do. If someone tells you that you are not good to drive, believe them. If you begin to argue with them over your ability, it's another sign that you have had too much. Invest in a cab or call a friend. Err on the side of caution.
You can invest in your own breathalyzer, which is a smarter move than relying on your own judgment and that of your friends. If you are taking this route, avoid the cheap models. If they cost the same as a discounted sweater, you can't really trust the results. Spend several hundred dollars to get one that delivers accurate readings. It can save you thousands of dollars of legal fees and fines and keep you from hurting someone else when you drive.
Of course, there are phone apps that can tell you if you are legally drunk. Nowadays, you can find an app for about anything. These apps will require that you buy a mouthpiece so you can blow into it, but they are a convenient alternative to a hand-held breathalyzer. These apps will also track your drinking patterns for you, which can alert you to potential excesses on your part.
Over time, you should have a good sense of your "limit," although how much you eat and how tired you are can make a difference in how you handle alcohol. Still, setting a limit of two drinks over three hours or something similar can help prevent you from becoming drunk.
Trusting your feelings when it comes to your ability to drive is always a bad idea. Sometimes the drunkest people are those who are most convinced that they are perfectly fine. Once you begin to drink, your judgment is impaired, so you need to protect yourself from you, the person with the potential to drive while intoxicated.
If you find yourself charged with a DUI, talk to a defense attorney like those at Stewart MacNichols Harmell Inc PS to see if they can help you overturn the case.