/timercheck is supposed to list all currently active timers when it's not. It worked for previous versions of mIRC, tested on 6.03 and earlier.
/timer 1 10 echo -a Hello!
/timercheck
Entering the above code will reproduce the bug.
mIRC v6.12
WinXP Home SP1
/timers
with no parameters
Edit: Although I just noticed that in 6.11 & 6.12, /timercheck returns "* No active timers" even if there are active timers running, where in 6.1 and older it works fine.
/timercheck gives the setting for the timer called "check", it was broken in previous versions and listed all timers.
From versions.txt:
10/10/2003 - mIRC v6.11
49.Fixed /timerN without parameters listing all timers.
From the mIRC helpfile:
To see a list of active timers type /timers. To see the setting for timer1 type /timer1. To deactivate timer1 type /timer1 off. To deactivate all timers type /timers off. If you are activating a new timer you do not need to specify the timer number,