Do you really like old-school Time ATAC alium (HP) pedals? If you answered yes, chances are you've had the same pair on eight different bikes dating back to 1996 and by now, though you wouldn't throw them out for the world, they're starting to get a little loosey goosey. Yes, ATAC stands for Auto Tension Adjustment Concept, but as Chevy has shown us with the Volt more than once, even a good concept needs a little help in tough times.
The basic idea here is that over time the spring holding your foot in gets bent or the body of the pedal gets indented, leaving play in the retention mechanism and letting you out a little too easy.
To fix it, we simply need to retension the spring and everything will work well again. (WARNING: this technique will add about 3g to each pedal. If you care, there's a pair of eggbeaters out there for you somewhere. You may stop reading now.)
Start by cutting a little piece of aluminum sheeting, which can be obtained at a hardware store in a variety of different thicknesses (try .5mm or thereabouts) into a rectangle. Then bend over the end like so:
note that the vertical face in the photo is actually curved a little. This is to keep the metal from buckling as you press it in. If you have a precision pair of pliers that can fold a small ridge on each of the vertical edges in the picture, that helps too.
Next, take your strip and slide it between the body and the spring (you'll see where the spring hits the body - slide it in there) on the side of the pedal that's loose:
Press or tap it in until the end sticks out the other side:
Bend the exposed end over the spring ends that you just squeezed past. This will hold your shim in place. If you want, you can also cut or break off the bent end on the other side, but it does no harm as long as it's below the level of the platform.
If your pedals are still loose after the first shim, simply repeat the steps above with a second one.