Check out Proc::Watchdog. Each process writes the current time to a file every so often. Another process checks the files every so often and if the time within isn't recent enough (process wedged/gone) it will alarm/restart/whatever. It might suit your needs. You can also try kill 0 $pid.

If SIGNAL is zero, no signal is sent to the process. This is a useful way to check that the process is alive and hasn't changed its UID. See the perlport manpage for notes on the portability of this construct.