I guess by "intrusion" you mean if someone bashes down the wall?
You're going to need more than a "pair", 60' is about 20m, so i'd say a cluster of about 25 5mm IR leds, and 2-3 IR receivers on the other end. You'd then use the IR receiver as a part of a transistor circuit to operate a relay or something.
That's just what came to mind, i'm sure there is an easier way of doing it... How about a laser pointed at an LDR? (Although alignment would be a pain) Haven't done this before, it might be completely flawed... something you could try? Red laser modules are cheap enough these days...