I use an explorer 2-but I think they are VERY similar.
Cryptodave is right in that you can progran it to only sound when you have the target area your after and as such don't need to see it. Bit if your like alot of people (me included) and like to back off a bit on dicrimination to let in other things the tones are easy to tell apart once you get the hang of it. Infact the thing basically writes a novel about the target every time. So much info-takes a while to understand the diference-but once you do it is AWESOME!
So summing up, you can use just tones and still get the info you need.
Hope that helped.
Have fun,
Salvager