Pilot refuses to fly after passenger smoked marijuana in lavatory

[goblin]

I think Kinder Surprise eggs are still illegal in US too, don't bring any for your kids... lol

They are now. They moved the toy to one half of the egg

 

[Nuclear_42]

I think there are various scenarios here that can happen. Did the passenger hide marijuana somewhere? Are lavatory alarms compromised? Who else has marijuana if that passenger managed to bring it? etc.
Maybe @Astro14 or @Just a civilian pilot can shed some light.

Lavatory alarms are very simple. They all communicate to each other via a smoke detector unit box (computer). Usually cycling circuit breakers clears the fault at the detector and the flight deck. When smoke is detected the lavatory module itself beeps, the flight attendants get a warning chime and flashing indicator light at their stations, and last but not least the flight deck gets an aural warning and displayed fault on their digital status pages depending on the aircraft manufacturer. Smoking on commercial aircraft is illegal and 99.99% guaranteed to get detected by the smoke detectors.