Setting node red from custom pollers

I'm not sure if im asking in the right place, but here goes

Im trying to set a node to red when an OID value changes - in this case the battery falls below 100% which means because we display maps this is then reflected on a map and know its on battery with say less than 70%

This can go into an alert and be triggered that way, using a script or something but havent come across anything yet, can anyone help please?

thank you Nigel