I bought the Graco Digital iMonitor Vibe . And I LOVE it! The only pit fall is it was about $60 which I thought was a little pricey... but I really recommend it. The sound is super clear- no static, plus when it detects a noise or a lot of motion it vibrates! Kind of like a cell phone. So in case I am doing something like vaccuming and wont hear my baby, I can "feel" her cries so to speak! It has a clip also and lights that light up and down depending on how loud the noise is. So pretty much it will let you know in multiple ways what your little one is up to, either by sound-sight-or touch! Its great.
Speaking of yard work , I do use it for this and no problems with signal. I clip it to my pocket and I always either hear it or feel it when my girl wakes up!