Especially with the Nest Protect smoke detector, I always found the interaction with Philips Hue lamps particularly exciting, even if the emergency hopefully never occurs: as soon as smoke and a possible danger is detected, all Hue lamps throughout the house should switch on. A function which, thanks to Works with Nest, could be implemented without any major problems.
Finally, someone has understood what it's all about. After numerous smart home systems have flooded the market in recent years, it feels like just as many standards have been established. Some systems work together, but other products cannot be linked. The Connected Home over IP project is intended to address this problem.