They put it up close to the head so the shooter will be sure to hear it.....with ear protection on it can be tough to hear at times. They can be set to give an "end" beep as well as a "start" beep. It depends on the course of fire to be shot. There are three types of scoring, comstock, Virginia count, and fixed time.
I found this as far as explaining them:
"Types of Stage - Virginia, Comstock, Fixed Time
There are three types of stage scoring method:
Comstock Count -- the most common
Virginia Count -- often used in classifier stages
Fixed Time -- the least common
Comstock Count courses of fire have no restrictions on the maximum number of shots that may be fired, no restrictions on the maximum number of times each target must be hit and no restriction on the amount of time required to complete the course. Each competitor may shoot at the targets until the competitor is satisfied with the hits on the target. Each target will require at least one hit on the target (usually two) and if there are more hits on the target than required, then the highest scoring hits are recorded on the score sheet.
Virginia Count courses of fire have restrictions on the number of shots that may be fired at the targets and on the number of hits allowed on the targets. The competitor can take as much time as is needed to obtain the proper number of shots fired and hits on the target. Shooting extra shots will cause a penalty of ten points for each extra shot fired. If those extra shots resulted in more than the specified number of hits on a target, each extra hit on a target is also penalized ten points.
Fixed Time courses of fire have restrictions on the amount of time the competitor has to complete the course of fire. There are also restrictions placed upon the number of shots fired and the number of hits allowed on each target. In most instances, not all competitors are expected to be able to complete the course of fire in the time allotted, so misses are not penalized. However, extra shots and extra hits are penalized as are no-shoot hits and procedural errors. Also, if a competitor fires after the amount of time to shoot the course has expired, each shot fired that is overtime earns a five point penalty. There is a 0.3 second grace period before shots are considered over the fixed time."