There are systems that send a trap upon failure, but no recovery trap. In such cases, manually resetting every single case isn't an option. Fortunately, we can construct a trigger expression that times out by using the function we just discussed—nodata(). An expression that would make the P state timeout after 10 minutes looks like this:

{Another host:snmptrap.fallback.str(Critical Error)}=1 and 
{Another host:snmptrap.fallback.nodata(600)}=0 

For now, we want to have more precise control over how this trigger fires, so we won't change the trigger expression to the previous example's.

Note that adding the nodata() function to a trigger will make that trigger reevaluate every 30 seconds. Doing this with a large amount of triggers can have a significant impact on the performance of the Zabbix server.