Probably a false alarm, but
possibly pulsed radar or VG-2
nearby.
Tone repeats slowly as you
approach a hill or bridge,
then speeds up sharply as
you reach it.
UNDERSTANDING RADAR AND LASER
RADAR SPEED MONITORING SYSTEMS
Three band frequencies have been approved by the Federal Communications Commission (FCC)
for use by speed monitoring radar equipment:
X band 10.525 GHz
K band 24.150 GHz
Ka band 33.400 – 36.00 GHz
VG-2
VG-2 is a Radar Detector Detector (RDD) that works by detecting low-level signals emitted by
most radar detectors. Your detector does not emit signals that can be detected by VG-2, but
does detect VG-2 signals and will alert you when a VG-2 device is in use near your vehicle.
While no signal is being detected, press and hold the Dim button for four seconds.
The factory setting for VG-2 alerts is Off.
LIDAR (LASER)
The correct name for the technology that most people refer to as laser is actually LIDAR, which
stands for Light Detection and Ranging. LIDAR operates much like radar. Its signal spreads out
like a radar signal, though not as widely.