In 1984, the police patrol uses helicopters to carry out its task. These helicopters can hover in between buildings in order to allow the police to look in through people's windows. Snooping allows the police to keep track of everyone and to maintain control over the populace.
In the story, young spies like Parsons' children work hand in hand with the police patrols. Parsons relates to Winston that his seven year old daughter actually followed a strange man for two hours one afternoon before handing him over to the patrols. When Winston questions why his daughter would do such a thing, Parsons proudly proclaims that his daughter must have found the stranger suspicious in some way. At the very least, he appeared to be a foreigner of some sort, as his daughter claimed that he wore strange shoes. From Parsons' story, we can infer that it really doesn't take very much to turn someone in; even extremely superficial claims can be enough to incriminate someone.
In many areas, the police patrol walk the streets in order to ensure that everyone maintains complete obedience to the dictates of the state. Anyone who appears to be doing anything out of the ordinary, even if it means just taking a different route home, can be stopped by the patrols if they run into them. The police will then demand to see proper identification and will proceed to question the individual extensively if someone has informed on the said individual's change of plans.
Sometimes, the police patrols also wait at railway stations where they will cross-examine Party members and demand to see their identification.