A gate or overhead door has one job the moment a vehicle arrives. It opens, and it opens without anyone touching anything. Motion detection is the most direct way to get that, and on most sites it is the right method. It is also the method most often specified for a job it cannot do.
The difference between a detector that runs for 10 years and one that generates service calls usually comes down to two things: where the sensor can physically go, and what happens when the vehicle stops moving. This guide covers what a car motion sensor actually detects, four site questions that narrow EMX’s line to one answer, and the point where motion detection stops being the right method.
What a Car Motion Sensor Detects
A motion sensor reports change. A magnetic probe reads a shift in the local magnetic field as a mass of metal moves past it. A microwave sensor transmits at a fixed frequency and reads the shift in the returned signal off a moving object. Both are comparing one instant against the next.
That carries a consequence worth stating before any model number. A vehicle that has stopped is invisible to a motion sensor. When the movement ends, the output ends, subject to whatever hold time is set. For free-exit, where a driver approaches, triggers, and drives through, that behavior is correct, and it is why free-exit probes are the cheapest reliable way to open a gate from the inside. For anything that has to know a vehicle is still sitting in the opening, it is the wrong physics.
It also means motion detection is an activation function rather than a protection function. A motion sensor tells the operator to open. Entrapment protection under UL325 is a separate device, a photoeye or a sensing edge, and no motion detector substitutes for one.
Dive Deeper: Work through EMX’s Vehicle Detector Selection Guide for the full decision tree across all six sensing technologies.
Four Questions That Narrow the Choice
Can you cut pavement? A probe needs a trench or a saw cut and a route for the lead-in. An overhead sensor needs structure at height and a clear view down the approach. On a finished drive with nothing overhead to mount to, this one question often settles the answer before any spec gets compared.
Do people and vehicles need different responses? A single-relay detector treats everything in the field the same way. Separating them lets a door respond to a truck while a light or a chime responds to someone on foot.
Is there traffic in the field you do not want? A parallel lane, a neighboring drive, or a sidewalk inside the detection zone will trigger an unfiltered sensor. Cross traffic filtering and directional modes exist for exactly this.
Does anything need to be detected while stationary? If the answer is yes, the answer is not a motion sensor. That’s presence detection, and it points at an inductive loop or the Loop Replacement System with DETECT-ON-STOP™, which holds detection on a vehicle that has come to a complete stop.
EMX’s Motion Detectors, Mapped to Those Answers
VMD202
A single-piece magnetic probe buried alongside the drive, electronics and all, in a 1 by 24-inch direct-burial housing with a 50-foot lead as standard and a 100-foot version available. The optional VMD202-R remote sets 10 sensitivity levels, and the setting holds in non-volatile memory, so the remote comes off the job and goes to the next one. Power is 12 to 39 VDC or 12 to 27 VAC at 70 µA standby, low enough for solar gate sites. As a field reference, a vehicle at 5 mph reads about 12 feet out from the probe.
Wrong choice when: underground power lines or a transformer sit near the probe or the lead-in run. Those shift the magnetic field around the probe and produce detections with nothing on the drive. Walk the route before anyone trenches.
CarSense 101
The same magnetic sensing split into two pieces: a control module on a standard 11-pin base with front panel controls and indicators, and a sensing probe buried along the roadway. That suits an operator or security board already built around plug-in detectors, and it lets a module be swapped without disturbing anything in the ground.
Wrong choice when: there is no enclosure or rack for the module. The probe also ships separately, so it needs to be on the order.
RAVEN
Overhead K-band microwave at 24.150 GHz, mounted 8 to 23 feet up, with a field of roughly 23 by 23 feet depending on height and housing angle. Two relays separate vehicles from pedestrians. Detection runs approach-only, depart-only, or bidirectional, with cross traffic filtering, relay hold from 0.5 to 300 seconds, and an IP67 housing.
Wrong choice when: a stopped vehicle has to hold the door open. Stretching relay hold time to cover that is a timer, not a detection.
OWL
The same microwave motion detection with an infrared presence channel added on a second relay. The motion field is about 23 by 19.7 feet, the presence field about 18 by 26.2 feet, and the presence hold is adjustable from 30 seconds to infinite. Mounting height runs 11.5 to 21.3 feet.
Wrong choice when: the mounting point is under 11.5 feet, or the direction logic has to be depart-only. The OWL’s unidirectional mode is approach. Its housing is rated IP65 against the RAVEN’s IP67, which matters on a washdown bay or an exposed outdoor mount.
Compare and Contrast: Both sensors detect motion the same way. Choose the OWL when something has to stay detected after it stops, and the RAVEN when it doesn’t and you want the tougher housing and the lower mounting floor.
Match the Detector to the Approach
Describe the drive, the mounting options, and what happens after a vehicle stops, and the choice usually resolves in one conversation. EMX has designed and built vehicle detectors in Cleveland since 1984, and the people answering the support line work in the same building as the people who engineered the product.
Find your local EMX distributor or contact our team to work through your site.