For sale is one brand new authentic LEGO light and siren piece.  You can only get these in certain sets as LEGO only includes these in a limited number of sets and doesn't sell them individually.  Each light and siren is tested before shipping to ensure proper working order.  They do have a sleep mode if not used for a long period of time.  Just hold down the button for about 10 seconds and it should continue to work normally.  Although you should have many great hours with this siren, the battery is user replaceable if it is ever needed.