Every time i lock my 2000 lexus RX300 by the remote the alarm goes off 15-20 seconds afterwards. I then have to unlock it and re lock it. or if i press the unlock button when i get out of the car the car will lock itself after 30 seconds but i am unsure if this alarm is then working. any ideas?

Vehicle Parts & Accessories - SMC - Alarm & Keyless Entry System for Toyota Vehicles