lax policy enforcement

A. How to steal a book from a library:

If you happen to take a book that has not been officially checked out the library has some sort of detector that checks if the item has been demagnetized or not (something that happens only when you officially checks out). in case the item has not been demagnetized an alarm goes off and a security guard asks for your receipt .. theres apparently a non trivial false alarm rate which entails the manual check.

however, heres a simple trick: officially check out item A but steal items B,C.... when the alarm goes off show the receipt for item A and the guard will let you go.

easy fixes:
1. always check all belongings when alarm goes off (high cost for consumers and security guard)
2. keep item A aside and make you walk through the detector again (if it still rings do step 1)


B. How to get free soda at a fast food joint:
simple thing is to ask for a cup for water -- they obviously wont deny you a cup. then you can easily get anything you want from the soda vending machine.

fixes:
1. make all filling (soda/water) go through a salesperson (i have seen these in some places)
2. have special water glasses that will make a loud noise if you fill anything else and thus serve as an embarrassing deterrent.
3. make only bottled water available!

in B the cost of implement it seems that the cost of implementing the fix is greater than the perceived benefit, so it probably justifies why stores dont care about the occasional guy stealing soda, but it doesnt seem to be the case in A (since a book/dvd lost means denying access to a potentially large userbase and high overhead in replacement etc).

P.S: I havent really implemented these attacks in practice :-)