Equipment Dependability

I've had 2 large systems, 50ish sensors.  1st SS2 and now SS3.  The only failure I've had was 1 of 3 cameras died after a couple years, but it was the original Beta Test camera that I took part in and was replaced under warranty.  Either I have good luck or you have bad luck.  The 3 year warranty tells me they have at least some faith in their products.

The only thing I had fail on my SS2 system was a CO sensor

I had the Master Keychain Remote and Keypad give me significant issues (SS2). It was just before I purchased SS3. To SimpliSafe's credit, they tried their best to find why I suddenly had so many problems, and the best guess was frequency issues from a neighbor (they installed something new around the same time). They promptly shipped out new components for both, and it immediately resolved.

That is the thing you can count on; the company will replace the sensors and components after troubleshooting without hassle. It was very reassuring.

SS3 has been stable, and the SS2 system I gave away has not had a single glitch. I do suspect, at times, some equipment will produce a bad batch (e.g., customers will report the same thing at the same time), but it is scarce.