You'll have to modulate the signal somehow, otherwise ambient light will influence it. Most IR receivers are the kind that things like TV's use, they receive a (nominal) 38khz signal and turn it into solid on or off signals on an output line. They however won't respond to either a solid 38khz carrier (as Nigel pointed out to me once) or to a solid IR light, they're not supposed to. So you'd need two 555's, one to generate the 38khz carrier, and a second one to turn the first one on and off and at much slower rate. The receiver will output a signal that blinks at the rate of the slower 555. If you do say 1khz as the 2nd 555's on/off speed you can connect a speaker up to the output of the IR receiver and you'll hear a 1khz tone when it can detect the transmitter.