Character repeation detection

[Tom]

Is there a function or package to detect if a character is typed
repeatedly? E.g. if a is typed 3 or more times in a row (aaa...)
then call a function.

Is there an existing solution for this? 

It would even be better if it had repetition suppression, that is
if I leave my finger on a key so I type a string of a certain character
(aaaaaaaaaaaaaaaaaaaaaaaaaaaaa) then after the first 3 repetition
the function is called and the rest of the repeated characters are
removed from the keyboard buffer.