When your radar detector alerts, observe the vehicles around you and what they were doing at the time and/or if they tend to be the same makes that accompany the radar detectors alerts.
The Escort Passport 8500 X50
is a fine radar detector. If top performance is your absolute priority, I would tend to shy away from battery operated models which tend to 'sleep' for very brief periods of time to conserve power.
However, if your radar detector alerting issue is an environmental one, you may experience similar behavior in your travels. Escort, I believe, has a 30 day evaluation/return policy
Keep me posted on your progress and good luck!