You play the part of a master cat burglar, no you don't go about stealing cats but you are very nimble and good at climbing. You have scaled the walls of the ferocious castle of Baron Von Ribboncable and avoided the pack of wolves he keeps as pets. You have picked the lock into the master display room and now you are standing in front of the display cabinet that contains the magic amulet from the last King of the Watomi tribe. The Baron stole this long ago and it is your job to restore it to its rightful owner. Well we can't have you playing the bad guy can we?
The only thing that stands between you and the treasure is an invisible infra red beam alarm, if it is triggered it will bring out a whole platoon of guards which is definitely not a good idea.
Fortunately you are a keen reader of the internet and you know that Grumpy Mike has said that the best form of alarm is triggered not on absolute levels but on difference levels. This prevents the alarm being triggered by changes in ambient lighting when the sun moves round the room. With your superior knowledge of electronics you know that if you move slowly enough you will not set off the alarm. Your task then is to remove the amulet without triggering the alarm.
Full details plus a video. :D