What technology do consumer clocks use to set themselves?

I picked up this alarm clock/phone/radio combination from a freecycler, plugged it in to the wall (power outlet only - not the phone), and to my amasement observed it set itself to correct date, year, and time (actually the time wasn't correct because of a change in daylight savings calendar, but I reset it manually). How come the clock was able to do that? Please explain to me how this works without making too much fun of me (if you can help it). Thanks!
I would have thought that if it picked up broadcast, it would have set the time correctly (with recent daylight savings change). The radio was off when the clock magically set itself...

There is a place for a battery inside, but there was no battery there. Internal memory?