I'm not a Tesla owner as of this post (but will hopefully would get one in the future), so I don't know about this completely. But so far, to me it doesn't look like the Model S has an alarm. There is no button on the keyfob, and when one of the show cars in the Tesla store was locked (note that the window was open), I reached in and pulled the interior door handle, and no alarm or anything went off. So my question is, is there an alarm in the Tesla Model S? If there isn't, I would know to buy an aftermarket alarm system if we hopefully get a Tesla in the future.