It depends on the context. In a 0 tolerance situation, any level of detectably alcohol percentage is considered under the influence. If you are asking about the per se limit for driving and passing a breath test, the level is set by the individual states.
40%
0.08%
Virginia law states that a person is considered to be "under the influence" if:He or she is 21 years of age or older and has a blood alcohol concentration of 0.08% or higher, or is under the influence of alcohol and/or drugs to a degree which impairs his or her ability to operate safely.He or she is under 21 years of age and has any measurable blood alcohol concentration (0.02% or higher), or is under the influence of alcohol and/or drugs to a degree which impairs his or her ability to operate safely.
40%
Yes, it is illegal to have the keys in the ignition while under the influence of alcohol, as it can be considered operating a vehicle while impaired, which is a DUI offense.
.08
0.08%
0.08%
0.08%
0.10%
.08%
.08%