Horn
- Not to be confused with Horn Deodorant.
The horn is a sound the player can cause a vehicle to emit for warning purposes. A horn is available for almost every land vehicle in the GTA series since Grand Theft Auto III.
Using the horn actually has no effect on traffic or pedestrians, but it is utilised in the mission Wear Flowers in Your Hair and used to attract other characters such as friends, characters in missions and prostitutes.
Some horn sounds are shared between vehicles within the same game, whilst others are unique. In GTA IV, a severe crash to the front of the vehicle will often cause the horn to sound.
In GTA IV, driving into a stream of heavy traffic and sounding the horn in the tune of Shave and a Haircut will lead to another driver responding with two beeps (two bits).
Sirens
Most Emergency Vehicles have sirens in addition to the horn. Holding the horn button will sound the regular vehicle horn, whilst tapping it will enable and disable the siren. Some vehicles also have a secondary siren noise sounded by holding the horn button whilst the siren is enabled. In some games, the horn button is sensitive, and trying to turn on the siren may cause the horn to sound instead. This was fixed in later games by forcing the player to hold the button for a longer time in order to sound the horn, but this comes with the side-effect of not sounding the horn at the intended time.
Where fitted, flashing lights or lightbars also activate when a siren is sounded. It is not possible to turn on the lightbar without turning on the siren, although in most games, if the player leaves the vehicle the lightbar continues to operate without the siren. A crash that affects the lightbar can cause the siren to not sound or sound incorrectly in GTA IV. Interestingly, using the Health, Armour and Weapons cheat, which also repairs the current vehicle, fixes the lightbar but the siren continues to function incorrectly until the player turns it off and back on.