Back in the day, I'm told that Geico would ask if you owned one ... and then promptly refuse coverage, saying that owners of radar detectors were more likely to speed and by extension be in accidents. I'm guessing things have changed since then ... that they want your money bad enough to not ask. If you're happy with them, well, that's great ... but I'd be cautious in talking with them and letting it drop that you own a detector.
BTW my annual premium on the ZHP with USAA is under $700, partly due to my age and a pretty clean (but not perfect) driving record. If you can qualify for USAA membership, its a terrific outfit with great prices.