Each bathroom with the SmartRestroom has a light above the stall indicating whether it’s in use: a green light means it’s available while red signals occupied. The software also has a counting sensor at the entrance of the restroom that tracks when passengers walk in and leave. Each airport can pick how many people enter the restroom before an email alert is sent to its custodial supervisor indicating that it’s time to clean the restroom — say, after 300 people.

[Source: NY Times. 5 October 2018]