Digging a bit deeper, there will also soon be something called "Nest Protect for Security Systems". Quote:

Nest Protect for Security Systems will be available in the first half of 2014.

This Nest Protect model is similar to the Nest Protect (Battery), but engineered to connect with existing security system control panels.

Nest Protect for Security Systems requires professional installation and will be available through the Nest Certified resellers.

Who knows whether they're planning to compete with them as well. I don't know, but I'd be happy to decommission my current home alarm system for something with Nest levels of spit and polish.

One last note: yee olde smoke and carbon monoxide detector, the fancy interconnectable ones, seem to cost all of $45/ea. The cheap fire-only ones that my builder installed seem more like $15/ea. Once again, Nest is charging significant more than "equivalent" products, but is getting away with it by virtue of building a better experience all around.