In the world of home security, the smoke detector has become an indispensable device. Its primary task is simple: to warn us of the dangers of smoke and possible fire. But this fundamental feature raises an intriguing question: How can we be sure our smoke detector will work when it's needed most? Here a fascinating paradox unfolds. Imagine that we install a second device next to our smoke detector, a 'detector checker', whose sole job is to confirm that the smoke detector is operational. At first glance, this seems like a logical step towards increased safety. However, if we follow this logic, how do we know that the detector controller itself is working properly? Do we then introduce a third device, a 'detector controller'?