I bought a Nest thermostat last year and in general have been pretty happy with it. We have 2 HVAC units in our house (upstairs/downstairs), but I've only only bought one for the downstairs primarily b/c of the up front cost. This problem seems to be exacerbated with a smoke alarm where most (or at least a lot of?) people will require multiple smoke alarms. My two-story house should have 3 or 4 detectors to cover all the living/sleeping areas, but even just one detector is enough of an investment to think twice before plunking down $130 per unit vs several of the $7.50 Kidde linked by jeanjq (<a href="https://news.ycombinator.com/item?id=6514777" rel="nofollow">https://news.ycombinator.com/item?id=6514777</a>). With the thermostat there's at least potential cost savings over time, but that doesn't exist with a smoke detector. Granted, the benefit of potentially saving your life in the event of a fire is priceless, but I think that convincing folks of the value here is going to be harder than with the thermostat.<p>Also, sensors in <i>any</i> smoke detector "expire" after some length of time (8-10 yrs - <a href="http://www.usfa.fema.gov/citizens/home_fire_prev/alarms/" rel="nofollow">http://www.usfa.fema.gov/citizens/home_fire_prev/alarms/</a>), so this is a semi-recurring cost. Also discussed in that article is the type of detection technology. This is using a photo-electric sensor vs a more traditional ionization sensor. Both have their benefits/tradeoffs, the ideal scenario seems to be to include both (slow smoldering fires vs hot and fast). (I've been researching these a bit lately for our house, would happily defer to an actual expert in the field though).<p>I love (and am tempted by) the technology and polish/ease of use that they've done here, but the cost seems to be more significant when compared to the current alternatives.