>relatively simple>pressure sensor, infrared heat sensor, CO2 sensor
we have very different definitions of "simple". and they need extra work to account for other use-cases (I cringe to use this term), such as lying motionless in a nice, relaxing bath.
a light switch on a cord works every single time, needs no maintenance, no firmware updates, the CCP can't spy on you through it, and you can make it look nice by hanging a decorative weight on the end.
a real "smart bathroom" shouldn't be about wallace and gromit gadgetry, it should be about making the experience more hygienic and dignified. such as: a bidet, rather than toilet paper.