There is a snooping module, to watch other's TTY activity.
One has to first load the snp module:
kldload snp
then request to watch another tty:
david:~>root@llanura:~ # w
10:06PM up 2:23, 2 users, load averages: 0.08, 0.21, 0.23
USER TTY FROM LOGIN@ IDLE WHAT
david...