Installation:
Drag and drop the plugins folder into your Grand Theft Auto V main directory.

Important(for LSPDFR users):
To avoid key conflicts, I highly recommend changing the following setting in your lspdfr/keys.ini file:
Change TOGGLE_SIREN_SOUND_Key=J to TOGGLE_SIREN_SOUND_Key=None

If you need to change the controls, you can do so in the BetterSirenControls.ini file.