Someone in a homeowners mailing list at my place of work said the following:
"Real alarm systems use what’s called supervised wireless sensors: if the sensor is jammed, the alarm goes off. Simplisafe uses unsupervised sensors, so if they get jammed, the central unit doesn’t receive any signal. Given that the Simplisafe frequencies are known, a sophisticated burglar can easily carry a wireless jammer and disable your alarm. The good news is that the majority of burglars are opportunistic and not sophisticated, so the risk is more theoretical than real. But you should replace your signs and decals, with the ones you can buy on eBay or Amazon. At least you are not advertising the brand of your alarm and its vulnerabilities, for people who might know."
I'm concerned about this, if it's true. Can simplisafe sensors get easily jammed in this manner?