I have to check the windows every night before bed by tapping the handles in order. I have to check the front door for as long as it takes to make sure it's positively, definitely, shut. I hold DH responsible as he has stumbled in drunk once or twice and left it open all night. We live in a relatively high crime area but thankfully got lucky and no-one noticed 
it has left me obsessed though.
Ever read 'A warning' by Dorothy Nimmo? It is daunting for anyone with these tics, I think.
A Warning
If when you have washed your hands you wash them again
though they are already perfectly clean,
if when you've checked you've got everything -
directions, cash, vaporizer, ticket - you go through
everything again just once more,
if when you are halfway down the street
you think you may not have locked the door
so you go back and yes, it is locked, but you wonder if
you remembered to switch the cooker off
so you go back to make sure,
I have to tell you it's likely to get worse.
Soon you won't be able to leave the house.
You will cram your bag with everything
you possess, you will hide it somewhere
absolutely safe.
You won't know where to put yourself.
You won't know what to do with your hands
so you'll steep them in pure bleach
but they are still offensive
so you pick up a knife.
You have lost your tongue. You have lost
your head. The cooker turns itself on
automatically, the burners are red-hot,
the warning light flashes
the sirens go off.
Sorry, not meaning to spoil your light hearted thread!! 