Want your gate to open automatically when you leave? A CP4 exit probe detects your vehicle as you drive toward the gate and tells the gate operator to open. No remote or keypad needed. Cartell manufactures the CP4, also written CP-4. You’ll also find it sold under other brands, including the LiftMaster 50-CP4 and US Automatic 070305. Depending on where you shop, it may be called a free exit device, exit probe, exit loop sensor, or exit puck.
The CP4 is a small, wired sensor that detects moving steel. It usually goes underground beside the driveway, with a cable running back to the gate operator. Although some listings call it an exit loop sensor, you do not need to cut a wire loop into the pavement or add a separate loop detector. The CP4 opens the gate for exiting vehicles. It is not a safety device and does not replace the gate’s required photoeyes, safety edges, or other protective devices.
Step 1: Pick the Right Location
Place the probe on the inside of the property, beside the driveway where vehicles pass on their way out. Cartell calls for 80–100 feet of separation from the gate operator. This also gives the gate time to start opening before the vehicle gets there. The vehicle needs to be moving for the CP4 to detect it. Cartell specifies at least 5 mph at the sensor, so choose a spot where vehicles are still traveling toward the gate, before their stopping point.
Think of the detection area as roughly a circle around the puck. When the probe sits at the edge of the driveway, about half that area reaches into the driveway, while the other half falls into the garden or ground beside it. At the factory High setting, Cartell lists detection at about 12–14 feet from the puck for a vehicle traveling 5 mph. That is the distance from the sensor, not the width of the whole circle. On a wide driveway, test vehicles using the far side too.
Cartell also lists these clearances:
- 6–10 feet from buried power lines, telephone lines, and invisible dog fences.
- 10 feet from natural gas lines.
- 20 feet from a power pole with a transformer.
- 100 feet from railroad traffic.
- 200 feet from high-power substation lines.
Step 2: Run the Cable in Conduit
Measure the full cable route, including the distance up into the operator’s control box. Choose a probe with enough cable to reach without stretching it or relying on an extra splice. Before burying anything, take a photo of the serial number on the bottom of the puck.
Cartell specifies 1/2-inch PVC conduit to protect the cable. Uncoil and straighten the cable before pulling it through, and pull gently so you do not damage it. At the probe, slide the conduit into the puck’s side connection. Do not glue the conduit into the puck. That connection needs to come apart if the probe ever needs service. This instruction applies to the connection at the puck, not every joint along the conduit run. Leave the probe and trench accessible until you have wired and tested the system.
Step 3: Wire the Probe to the Gate Operator
The normal setup uses two wires for power and two wires for the opening signal. Turn off operator power, including backup power as directed by its manual, and unplug the separate power supply before wiring.
Two wires for power: red and black. For a gate with a 115V outlet available, use a separate plug-in low-voltage transformer or power supply. Connect red and black to its low-voltage output. The CP4 accepts 8–24 VAC or 8–30 VDC. With DC power, red goes to positive (+) and black goes to negative (−). For a solar gate without a 115V outlet, use the operator’s approved DC accessory power terminals instead, following its manual. Two wires for the opening signal: blue and white. Most gate operators use a normally open (N/O) contact and common for the exit command:
- Blue: Connect to the designated Exit or Open input.
- White: Connect to that input’s Common or COM terminal.
Use the exact terminals shown in your gate operator’s manual. The yellow wire is unused in this setup. Insulate its end.
Step 4: Keep the Factory Setting and Test
Leave the sensitivity on High, the factory setting. There is normally no need to open the puck or change anything inside. Restore power and keep the puck stationary at the planned location. With the gate’s travel area clear, drive a vehicle past the probe on the path you normally use to exit. The gate should receive an opening command as the vehicle passes the sensor. Wait for the gate to open fully before driving through. Repeat the test with the vehicles that regularly use the property and across the parts of the driveway they use.
Moving a piece of steel near the puck can confirm that it triggers, but it does not replace testing with an actual vehicle. The CP4 sends a brief opening signal. A vehicle parked beside it will not reliably hold the gate open. If the probe misses vehicles or picks up traffic outside the intended area, check its placement and wiring before burying it. Use Cartell’s manual for troubleshooting if needed.
Step 5: Bury the Probe and Test Again
Once the probe works correctly, finish the installation. Cartell’s burial diagram shows 5–8 inches of soil above the top of the puck. Pack the soil firmly around it so it cannot shift. Movement of the puck itself can cause unwanted gate openings. Keep the cable protected in conduit and complete the conduit burial according to applicable requirements.
Cartell also allows above-ground installation when the puck is screwed to an immovable object. The cable still needs conduit protection. After backfilling, repeat the vehicle tests. Confirm that the probe picks up the intended exit path and that the gate opens consistently. If something changes after burial, check the puck’s position and stability.
For a closer look at the installation, watch Cartell’s installation video on our CP4 product page. You can also download the CP4 installation manual and CP4 specifications.
Getting the location, cable protection, and wiring right makes the rest of the job easier. Test before covering everything up, then test again when the installation is finished. Find the Cartell CP4 exit probe at Elite Gates. If you need help choosing a cable length or matching the probe to your operator, have your gate operator’s model number and cable-route measurement ready so our team can help you get the right setup.