Most shifts begin with a briefing or roll call session of 10-30 minutes. Here, a supervisor will assign beats (patrol sectors) and radio call numbers, advise of any special details or assignments that might have to be covered during the shift (e.g. a high school football game is set to end at 10 p.m., and an officer should be in the area for traffic control), and brief everyone on any ongoing crime patterns or "BOLOs" (Be On the LookOuts) so officers will know to watch for specific behaviors, people, or vehicles. Briefing frequently incorporates some brief training material on new case law, gang activity, symptoms of drug abuse, or other topics. The briefing session may include an inspection of everyone's uniform and equipment.
The officer then goes to his assigned patrol car and inspects it for function of all regular and special equipment (headlights, turn signals, emergency lights, siren, etc.) and to replace any missing supplies from the usual complement of first aid kits, road flares, crime scene tape, fire extinguisher, etc. The officer uses his radio to report he is "in service" to the dispatcher and begins his patrol.
If the officer is working during the weekday, he may be called into court to testify on a case from a previous shift weeks or even years before. If he works at night or on weekends, he may be called into court during his off duty hours. He will be paid overtime if this happens. When he plans a vacation, he has to notify the local prosecutors' offices of his planned absence so they can request continuances for any cases set to be heard during that time.
When not assigned to a call for service, officers are generally free to roam at will within their patrol sector and initiate any activity they see as worthy. This includes stopping cars for traffic violations, interviewing suspicious-looking persons, investigating conditions that are JDLR (Just Don't Look Right) for evidence of criminal activity, and chatting with businessmen and neighborhood people. If the officer has a patrol car computer capable of making inquiries to the various criminal databases for police, such as NCIC (National Crime Information Center), he may check the license plates of cars he sees to determine if they are stolen or the registered owner is wanted. Good patrol officers have a high level of "on sight activity" and are seldom idle or driving aimlessly for very long.
At some point, the dispatcher will notify the officer of a call for service, either by voice radio or by sending the call in text to his patrol car computer. Calls for service can be just about anything: domestic quarrels, thefts from a business or home, burglary, a vehicle accident, or just a citizen with a question or concern. People will call the police when they don't know who else to call, so a good patrol officer knows the available resources in the community and how to reach them. It's highly likely the officer will spend more time on these public service and order maintenance matters than on actual law enforcement.
If a call for service requires the filing of a report, the officer may complete the report in the field or return to the station. Most officers with patrol car computers can file paperless reports from the field, but this requires sitting in the car for extended periods in a posture not conducive to typing because of the space restrictions in the car. While typing the report, the officer can also lose his sense of situational awareness and not notice a potential hazard approaching him. This is why officers will sometimes park in the middle of a large, empty parking lot or other open space while doing paperwork. The buffer of the open space makes it difficult to approach the officer's car without him observing the approach.
The officer may also have to go to the station to book evidence related to a case. If an officer recovers narcotics or physical evidence at a crime scene, he has to protect the "chain of custody" and document the location and status of the evidence from the time it is recovered until it is introduced as evidence in court. If the evidence is left unattended in