How do you use police light and srines in gta4 PC?

In GTA IV on PC, you can activate the police lights and sirens by pressing the "H" key while driving a police vehicle. This will turn on the lights and activate the siren. You can also use the siren for different sounds by pressing the "Q" key, which cycles through various siren tones. Be mindful that using these features can attract attention from other pedestrians and vehicles in the game.