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I suspect that, if you do not have an improperly mounted Dakota 3000 Wireless Alert device, or one that is simply not working properly, you may need to turn up the sensitivity setting. (The sensitivity setting is # 3, in the illustration on page 3, of this documentation:
If the sensor is mounted too high off the ground, you see, it will not detect all vehicles that don't have a sufficient heat signature higher up.
Also it helps if the sensor is pointed somewhat down the driveway rather than directly across it.
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