The failure of a V1 to alert to the Hot Wheels Radar Gun might have one of several causes:
1) The hot wheels radar gun may have drifted out of the police radar band. "Part 15" devices are somewhat notorious for this behavior.
2) The V1 in question may need to be sent to Valentine Research to make sure it is operating correctly.
3) The hot wheels radar gun may employ a modulation technique (such an FM-CW pulsed etc) that the Valentine rejects. Although such techniques are allowable for other devices (part 15 etc) they are not used for police radar.