I was able to get an answer from an online seller of Silpat about why my brand new Silpat set off my fire alarms for twenty minutes.
He said sometimes the manufactur rush the process and does not completly "cure" the silicon, and that's why I smelled burning rubber and my neighbors thought I was burning down the house. He suggested that I take out the batteries in my fire alarm and set the oven temp to low and cure the Silpat myself. After all the silicon burns off, it should have no further problems. I, however, am not going to attemp that myself, so have called William Sonomas (from which this particular piece came from) and they had offered to exchange mine with no hassles.