TJ Campie wrote a post on his blog detailing his DIY SWR indicator/bridge build:
Dan Tayloe, N7VE, developed a really neat resistive SWR bridge that uses a simple LED to identify the dip in SWR on an antenna. QRPkits.com sells a nice kit of the bridge for just $15 and I recommend that if you don’t already have the parts in your junk box. I got really lucky and found some 57 ohm resistors in an old shortwave radio I tore apart and I had the rest of the parts in my junk box (minus a DPDT switch).
Kind of reminds me of the old grid dipper.