Properly trained L.E.O's etc will find everything. They ain't the problem.
Terrorists (who are)ain't going to search people in the short term. Long term - yes.
Basic rule is to escape at the first oppotunity. If they say that they will kill "x" no of people if someone escapes? Escape anyway. If your are a Brit Cit or an Amercan your probably going to be killed anyway.