Door and window sensors can be bypassed

@kenmoreno old news and falls under the category "don't believe everything you see on the internet.".  Besides Simplisafe's official response, I did my own testing like I always do.  (My favorite was the invisible dog fence hack, fun to test and debunk.)

As far as this one, yes, it is true you can defeat SS3 as described, but there are a few big IFs with that. First, the intruder has to know you have SS. (I use a generic sign but they can read my doorbell). The 2nd one, which is a bigee, the intruder MUST know the exact location of the sensor to be defeated and the location of the base. This is also can be defined at the "line of sight". If they know that (which would have to be an "inside job", yes the "simple device purchased for $20 on Amazon" - which I paid 7 bucks- can block the signal.  

Did extensive testing and could block it every single time I placed the fob  in the direct line of site. If not, alarm went off and, if I wasn't in test mode, the monitoring center would have dispatched.  BTW, the base will report to you interference when detected too.

You can read all about this in the forums by using a google site search. Simplisafe, you said you are working on a new forum site, please make topics like this discoverable so customers who just discover them don't panic! And Simplisafe Social Team, suggest you link your response here in this thread.

By the way, this "weakness" is intrinsic in every single wireless brand out there.  There is no way to avoid this in a wireless system.  Well, that's not strictly true; if every sensor transmits with 20 Watts of power, you probably couldn't jam it.  Of course, you'd have to replace the batteries in every sensor every 10 minutes.  :-)

If the transmitters are "spread spectrum" they are much harder to block.  I don't know if Simplisafe's transmitters are, but Ademco's definitely are.