How do condo associations handle emergency access to units?

We are small (<40 units) self-managed beachfront 5 story condo building that is used almost exclusively as a vacation property or second home. As the building ages we are finding a need for access to more units to inspect for water leaks in order to identify and/or take corrective action to minimize damage. We have the standard practice in place to turn off the main water valve when units are not occupied but that is not sufficient because some leaks are not known or detected until damage is detected in a unit below.

We are wondering - what type of polices or practices have other condo associations implemented to address emergency access to units? If you have a process in place, how are individual unit keys secured and made available for unit inspections, especially when you have no resident agent? Please identify any control or liability issues you have addressed.