1) Give a description of the problem
I have a piston that shuts the light off in the bathroom after 2 minutes of no motion. However, this will turn off the lights while I’m taking a shower.
*2) What is the expected behavior?
I was wondering if I could create another piston that was triggered by a routine that I can call from an Amazon Echo that would interrupt or stop the execution of my motion piston.
Create a virtual switch called “Shower”, in your piston use that switch as a condition.
If Shower switch is off allow piston execution.
The virtual switch you can turn on/off using Alexa.
With the default cancellation my light always stays on until I leave the bathroom.
Do you have something modified in the policy?
The issue is that when I’m in the shower, the motion detector doesn’t sense any motion because my curtain is completely opaque.
I have the same issue in the early days. I just lengthened my time out a bit and raised the sensor to catch my head. I’m 193 cm, if you Napoleon your mileage may vary 
As a safety net, it might be worth making another small piston to reset your Simulated Switch (Shower) after X minutes. Something like:
if Shower has been on for 30 minutes, turn off Shower
This will save you from having to tell Alexa to turn it off after you are finished.
