mp.keys.bind(0x42, true, _ => {
    mp.events.callRemote("keyPress:B:toggleSiren");
});

mp.events.add('toggleVehicleSiren', (vehicle, state) => {
    vehicle.setSirenSound(state);
});

mp.events.add('entityStreamIn', (entity) => {
    if (entity.isAVehicle()) {
        var state = entity.getVariable("sirenSound");
        if (state === undefined) return;
        entity.setSirenSound(state);
    }
});