Whilst cities in Grand Theft Auto, Grand Theft Auto: London 1969 and Grand Theft Auto: London 1961 have other emergency services, as a criminal the player is more likely to draw the attention of cops, especially after committing various crimes. Their degree of hostility and enforcement towards the player is determined by the player's wanted level, which is considerably rudimentary when originally conceived.
Generally speaking, any crime committed (including hit-and-run, firearms discharge, collisions with vehicles, vehicle theft, etc.) will eventually lead to the player attaining a wanted level, regardless of whether or not a police officer is on the scene; on occasions, police radio chatter can be heard following a crime the player commits. If the player breaks a law within earshot of a passing police officer or a moving police car, they will instantaneously receive a wanted level. The more crimes the player commits, the higher the rating goes. Also, sometimes the player automatically gets noticed, if a mission leads to someone calling the police, or in the case of bank robberies that not surprisingly put the police on full alert.
The police's aim is in general to arrest the player, although they will not hesitate in shooting or trying to ram them off the road in the desperate attempt to stop the player, and they get more trigger happy the higher the wanted level. On arrest, the player is dropped off at the nearest police station, losing all weapons and armor and half of the score multiplier, but the wanted level is reset back to zero.
The player's wanted level, which reflects how much attention the police give them, is simply illustrated by one or more police heads on top of the screen (in GTA, the police heads are those of generalized American cops with peaked caps, while those in GTA London are distinguishable by their signature custodian helmets); the heads bob in an up-and-down motion if the player is in sight of one or more police officers, but remain stationary when the player evades the police. This feature was carried over to Grand Theft Auto 2.
At the start of the game, the player has no wanted level and the player is ignored, but when the player commits a serious crime, this warrants the cops paying heightened attention to players, and the wanted level correspondingly increases, up to a maximum of four police heads. At wanted level one, the police tend only to give chase if they are in the area anyway (unlike GTA 2 and its successors, even a single wanted level will not disperse on its own), whereas at four, the police set up roadblocks on major roads, shoot on sight, and send all available units to the player's location.
There are only two ways the player can evade the police, as hiding in alleyways or other areas inaccessible by cops will not make a Wanted Level attained to disperse on its own.
Dotted around each city are a number of respray shops (if one of the cities are large for inexperienced players, then finding it will be difficult), where the player's vehicle can be resprayed, or have the license plates changed, to disguise it. This makes the police think the player is someone else, even if they see the player enter the shop, although this does cost money (i.e. points). The higher a player's wanted level, the more points it costs to have a car re-sprayed or plates changed.
An alternate method is simply to locate and acquire a cop bribe, which can be found in specific breakable crate in any city. Although the pickup is cost-free, its rarity makes this approach equally difficult as each bribe is a one time only use. Another similar pickup, the "Get Outta Jail Free Card", allows the player to avoid the pitfalls of being arrested by having the player retain their weapons, armor and multiplier as of the time they were arrested.
- One head - This is displayed when the player commits a "minor" (by the standards of GTA) crime - such as shooting/running over a few pedestrians, attacking a police officer or exploding a car. One police car is sent to your last known location, eg. they check the wrecked car or the place of the murder. A maximum of one police car chases you, and police run slower than the player. Despite having only one head, the only ways for it to disappear are to either drive to the respray shop or pick up a police bribe, as simply attempting to hide will only make one head remain stationary.
- Two heads - Very similar to one head. Now, police can use a maximum of two police cars to chase the player and will either shoot or arrest the player on sight. This level is reached by committing a series of crimes - destroying more cars, killing two police officers, or a few more pedestrians.
- Three heads - The first "serious" wanted level. Now, police will form road blocks manned by armoured officers armed with pistols. 'Normal' police will run at full speed, and will be a little more bulletproof. They will deliberately force the player off the road and will either kill him or arrest him. To reach this level, kill as many police or pedestrians as you can.
- Four heads - The police is now more aggressive at this level, as pedestrians start to disappear from the streets. At this stage, the player is very vulnerable outside of a vehicle. Also, police officers will use Machine Guns from now on to shoot the player.
- The imagery of the police heads' bobbing motion when the player is in sight of police officers seemingly references the term "bobbies", a British slang for police officers.