Fun computer science puzzle

[CcXD]

So I have been trying to figure this out for a while. Its a fun puzzle game that might send you thinking for a while, here it is:
Lets say you work at an office/lab, and you have workmates. Lets also say that you love Coke, so much you always have a 6 or a 12 pack at the office's fridge. Whenever its empty, you just buy a new one. But one day you suspect that one of your co-workers is stealing Cokes from you, and you dont appreciate that. Now, you mission is to Create some sort of algorithm that will let you know if someone is actually stealing your cokes or not.
For the sakes of the game this is how the 12 Pack looks like:
_______
|000000 <--
|000000 <--
'''''''''''''''''''
Where the Right side(arrows) is the part of the box that is opened. the 0 are the coke cans viewed from above.
Here are some rules that might make the game a bit more fair:
-The algorigthm is designed to verify whether someone is stealing cokes from you, NOT to know WHO that person is.
-You can design your own initial conditions.
-No memorization (not counting cokes everytime, not keeping records on how many you take)
-It has to be something relatively simple, that is, no super complex location of the cokes, in a super complex way, keep as simple as possible.

Remeber, you have to know immediately once you open that fridge and reach for that coke, if someone has taken one already or not. I have my own answer, but ill wait a few days to see what people say.
Well hope u like this game.

[Rashakil Fol]

This game sucks; do your own homework.

[Ezzaral]

If you can't keep track of 6 or 12 cokes and your own rate of consumption well enough to tell if someone's stealing them, you certainly aren't smart enough to figure out an algorithm for it. You probably aren't even smart enough to be working there at all.

[Ash Abe Add]

Heh this is neat. I think I know but I'm not sure if it go against rules, for memorizing.. But here an idea, If this is a 12 pack and it the one where only the top part is open. Then you put a marker on it. So to say the marker will fall off if it is rub against the can box. So when someone pull a can out the can will push the marker down and you will feel it not there. The marker can be like a sticky pad on the top side. That way it will be rub off and the culprit won't know where it goes, since he/she/they is/are in a hurry. and when you check you won't feel the texture of the note pad.