Justin wrote:

Hello,
After locking myself out of my apartment yesterday, I managed to make
the problem worse by fiddling with a piece of plastic in the lock
which broke off and ended up being shoved pretty far into the back of
the key hole. I tried using some needles to get it out, but no dice.
Anyone have a reasonably cheap solution?

Try a piece of coping saw or fret saw blade. [if you've been able to
poke the plastic back in, maybe a *hot* needle would pierce it, let it
cool and see if they bond, and pull gently.]

Would injecting acetone
damage the mechanism in any way?

The acetone might not melt anything in the lock- but if it melted the
plastic it would most likely gum things up enough so the lock would be
useless.

If the saw blade won't get it, I'd try [long shot] blowing canned air
from the other side--- then I'd take the cylinder out, bang on it a
while- and if all else failed, take the cylinder to a locksmith and
watch him pluck that plastic out in 10seconds.

Jim