Ken,
For the most part I agree with you that the responsibility should be with the owner.
However, we don’t want to leave a home when it is unprotected, even if it is at a time when an alarm could still easily be purchased (during business hours, which for that is about 7am-9pm every day…).
We will likely also incorporate a “fee for service” in case an alarm has not been purchased in the appropriate time, stated on the loaner form, or depending on their demeanor, issue a ticket.
Part of the reason for this is, especially with CO alarms, that we could deal with a faulty detector, not just people in non-compliance