In 0.4, when you witness a crime taking place, or when someone resists or attacks you, you can 'call it in' by holding B (by default on keyboard). This will initiate a Pursuit of the suspect and allow other officers to be called via the Backup Menu to assist. Additionally, any officers already in the area will be alerted.
The player 'calling in' a PC 148. In this example, the suspect (in red) has fled an attempt by the player to Stop & Frisk them.
The Backup Menu contains all the various options in LSPDFR for calling for assistance. It is access by pressing B (by default on keyboard) or Right Stick (by default on controller).
The backup menu on LSPDFR 0.4.
The Backup Menu can be filtered by Agency. This means that only units belonging to the chosen Agency will be shown. If the agency is set to None - the closest available unit for the type that you request will be dispatched. You can set a response location by using the waypoint marker on the map.
Code 2: A less urgent response, lights and sirens are only used to clear heavy traffic.
Code 3: An urgent response with lights and sirens.
Pursuit (only available in a pursuit): The same as Code 3, but with the intention of responding to a pursuit in progress.
Transport (only available after setting an arrested suspect on the ground): The same as Code 2, but with the intention of transporting an arrested suspect.