This probably isn't too rare for apartment buildings, but my building has certain emergency lights that aren't usually on and can't be switched on by the residents, but they're hooked up to a special emergency generator. So paradoxically, if you see that they are on, you know there's been a power failure. I came home today and saw that these lightbulbs had tripped on. Those and the lights behind the EXIT signs, which are apparently indispensable either way.
Needless to say I wasn't too happy to find out that we were without electricity on what will probably be one of the hotter days of the year. But there was nothing to do for it but wait for the guys from National Grid--who were already working on the street--to fix it. I read outside while waiting. At one point I looked up at a neighbor's window fan and saw the blades spinning, but it turned out that the wind was blowing them, then it would stop. But after some time I poked my head in and saw that it was dark. Again paradoxically, this was a good sign.