  This short note is the result of a French "Hippocampe internship" that aims
at introducing the world of research to young undergraduate French students.
The problem studied is the following: imagine yourself locked in a cage barred
with $n$ different locks. You are given a keyring with $N \geq n$ keys
containing the $n$ keys that open the locks. In average, how many trials are
required to open all locks and get out? The article studies $3$ different
strategies and compare them. Implementation of the strategies are also proposed
as illustrations of the theoretical results.
