When a law enforcement officer pulls you over for suspected drunk driving, he or she must have some reasonable cause to do so. Generally, this will be evidence gathered by watching your actions as you drive.
MADD explains there are various ways you could signal you are not sober enough to be behind the wheel. Some of them could be very obvious, but others may be subtle.
Obvious signs you are drunk include actions that make no sense or that put you in danger. For example, driving on the wrong side of the road makes it clear something is not right. Another example is swerving into the other lane or hitting objects alongside the road.
Other actions include driving without your headlights when it is dark or driving over the center or sideline on the road.
Subtle signals may require an officer to watch you drive for a while before it is clear there may be something going on. Examples include slowing down or speeding up very quickly, stopping randomly or not stopping quick enough at lights or stop signs.
You may also make an officer pay attention if you are driving very slowly with no apparent reason or making abrupt movements, such as a quick turn, continuously. Tailgating also is often a sign of drunk driving.
Most of the time, an officer will watch you drive to get an idea of whether something was a one-time thing or if you continue to display the behavior. Once an officer pulls you over, you should expect to go through tests to determine if you are driving drunk.