This is sort of a flimsy suggestion, but tcsh has a built in method for watching other users logging in and out. You might have a go at joining their mailing list and asking how they do it.

.tcshrc clipping:

# Watch any(1) other users every 0 seconds from any(2) console, 
# when logging in/out.(I like this one!)
# It gives something like "root has logged on tty1 from local."
# You may find it annoying on busy systems (like shell1.sourceforge.ne
+t)
set watch=(0 any any)

# Format of output string when someone logins or logouts.(Look above)
# Hmm, can't be internationalised easily.
set who="%n has %a %l from %M."
[download]

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naChoZ