It can take up to and hour for your monitor to go blank like that. For that hour or so, your monitor is giving your readings (PSI/temp) from stored memory.
Test yours and see how long it takes. Take your monitor with you and drive a distance you know is out of range of your sensors. See how long your monitor continues to give you readings for your out-of-range sensors.
Our monitors don't have a signal strength indicator. Nor is there a user setting that would let us say "Don't wait an hour to tell me a signal's sensor has gone missing". (Our manual has some poorly worded mention of it - on page 8 I think.)
Alot of things other than length/distance can interfere with a signal's sensor. Supposedly a repeater/booster helps make signal loss less likely, but who really knows.