What the check-in actually consists of
A start message when the cleaner is on site and inside, an expected finish time, and a finish message when they leave. It is deliberately simple because a complicated system will be abandoned within a month. The value is entirely in the third element: the defined action when a finish message does not arrive, since without that the first two are just messages that nobody reads.
That action needs naming in advance. Usually it is a call to the cleaner, then a call to the client's after-hours contact, then attendance at the site or a call to emergency services depending on the circumstances. Writing it down means the person receiving the missed check-in does not have to invent a response at midnight, which is when hesitation is most likely. Hesitation is the failure mode, and a written action removes it entirely.
