That is what I'm saying. If the skin you are using doesn't allow the selection of alerts to be displayed and/or announced, then the only way is to only have the alerts that you want in speedcam.txt via filtering. What skin are you using? I don't have this problem with dimkaWa skin. Note that alert settings work only when you drive, so after changing it "nothing change at screen, and still appears ALL type of radars" until you drive.
You can try to add the following to sys.txt (make sure you removed other similar entries or start out with a clean sys.txt)
Spoiler: .
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