I have the same problem when we have company and they use the spare bath. Believe it or not, I think my Son-in-laws' aftershave sets the think off!
Can you move the unit further away from the bath? Does your bath have an exhaust fan and do you use it?
Moving it should be easy if it is a battery operated unit. If it is hard wired, one option would be to replace it with a battery operated unit placed further away from the bath. Or prefered, have an electrician rewire for a better location.