What is the condition?
I have used
a specific string received on the serial
TxD pin held low
a certain combination of pushbutton presses

so, the naswer is : "whatever you want it to be"

Where do i put the call?
where the condition you have chosen is detected

In addition to the 'all ok' location (e.e. triggered by a string) I suggest you you add 'the backdoor' (very helpful during developemnt) test the Tx (or some other) pin right at STARTUP: in startup.a51 and call NoTouch if the pin is held low.

Erik