The Radar Sentry enjoys it's prestigious place in history as (for all practical purposes), the first commercial radar detector! A LOT more history and data on the Radar Sentry can be found on the Radar Sentry on our page about The First Commercial Radar Detectors.
This particular Radar Sentry is a "transitional" unit. It seems to have been made soon after the patent was granted, but still using the older face plate with the "Patent Pending" at the bottom.
Notice the "patent pending" at the bottom.
The antenna is "angled" like most later Radar Sentrys.
Note the patent number at the bottom of the back..