I don't know a lot about this ELB stuff, so I'll defer to Jaba.
So cruising at 1000' agl I have an engine failure.
You're going to hop onto 121.5 and give your position (assuming your position device is still working) with only a few seconds to impact? Activate your ELB.
BTW, you did you put in a flight plan so that the services would know here to look regardless of what warning you get out, didn't you?