I've seen (and heard) of them advertised.
When I bought a house in 2012, I looked into a DIY security system and decided on Frontpoint. I highly recommend them. You have to buy the system. I think it was around $300 depending. You call and tell them, I have 3 doors, two windows, 2 motion etc. They also do cameras, fire alarms and thermostats. They pre-configure the system for you. All you do is stick the sensors on the doors, walls and windows. It's totally wireless. The sensors communicate with the panel wirelessly and the monitoring is totally wireless. The monitoring plan I have is a little pricey at about $42 a month but you can arm/disarm from your phone or PC and it has tons of other features. Also the monthly fee includes the wireless connection (phone line) so if you consider that, it's reasonable.
https://www.frontpointsecurity.com/
As for Simplisafe, I think they sell a comparable system and if the monitoring is less I would definitely be interested. You need to compare apples to apples. They do advertise the monthly fee at around $25 but I don't know what it includes.