What A-Red said is worth thinking about, but if you still want to give it a shot keep reading. Do the following and adjust it to match your needs. In
this thread I describe how to use the Math action. It might help.
GEOM. Find Hurt Units
Monsters (subj)
Health Fraction Less Than
Entire Map
Tested Items Inside Field Name
Results Action Identifier
Activates on Failure "Increase Health Check"
Activates on Success "Reset Health Check"
MATH. Increase Health Check
Left Action Identifier "Find Hurt Units"
Left Field Name "hef<"
Add
Right Decimal Number "0.01"
Destination Action Identifier "Find Hurt Units"
Destination Field Name "hef<"
Activates on Execution "Find Hurt Units"
MATH. Reset Health Check
Left Decimal Number "0.01"
Destination Action Identifier "Find Hurt Units"
Destination Field Name "hef<"
Activates on Execution "Find Hurt Units"
Make the GEOM's expiration mode to be "on execution". In the GEOM, for the "Monsters (subj)" parameter, add all the possible units you want to run this test on. For "Health Fraction Less Than", add a small value for example "0.01". You might need to play around with that to see what is best for you. Keep in mind for that parameter 0.0 means no health and 1.0 means 100% full health. If the location of these units does not matter, then "Entire Map" is what you want. If you only want to check near certain locations you will need to use a Polygon or a Circle geometry.
For "Tested Items Inside Field Name" it depends where these results will go. If these units are "Targets" in an Attack action then you will use "obje". For "Results Action Identifier" you will put the action you want these results to go. For example, you can put them into an Attack action.
For "Activates on Failure" you will put the "MATH. Increase Health Check" action. This will alter the "Health Fraction Less Than" value when no units are found with that much health. For "Activates on Success" you will put whatever you want to happen when it finds a unit with that little health. Also you will want to activate the "MATH. Reset Health Check" action. This will reset the value back to a low number. This way it can run a new test and find hurt units that might have gotten damaged when the GEOM was not running.
Whatever you decide to use for the starting "Health Fraction Less Than" value use it on the "Reset Health Check" Math action as well. In the "Increase Health Check" Math action I used a value of 0.01 for the increments, but you can change that to whatever you want as well.