The counter category that sees shape, not faces
A Time of Flight people counter is an overhead sensor that counts entries and exits by measuring distance instead of capturing images. It floods the doorway below with invisible infrared light, times the reflections, and builds a live depth image in which each passing person is a distinct three-dimensional shape. Software tracks those shapes across a counting line. Nobody is photographed, because there is no photograph: the sensor records geometry.
Why choose ToF over a camera counter?
Three reasons come up in every deployment. First, privacy by construction: a depth sensor cannot produce footage, faces, or anything a GDPR assessment treats as biometric material, which shortens legal review and works-council conversations alike. Second, light independence: the sensor brings its own illumination, so a dim entrance, a glass frontage at sunset, or a fully dark after-hours doorway all count identically. Third, shadow immunity: mono cameras can count shadows and reflections as people; a shadow has no depth signature. The full comparison is in computer vision vs ToF for people counting.
How it works, briefly
The sensor mounts on the ceiling just inside the entrance, looking straight down. Each frame, it measures the distance to every point below. A person entering appears as a head-and-shoulders silhouette rising out of the floor plane; the software tracks each silhouette's path and increments the in or out count when it crosses the virtual line. Because the silhouettes are three-dimensional, two people walking shoulder to shoulder separate cleanly where a beam counter would register one. The sensing principle behind all of it is covered in the ToF pillar explainer.
Six things to check before buying
- Mounting height and coverage. Every ToF counter has a specified ceiling height range and a footprint it covers at that height. Ariadne's ToF sensor mounts at heights up to 3 meters; wider entrances take multiple units working as one line. Get the door widths and ceiling heights into the site survey first, because they decide the hardware count.
- Group separation. Ask how the device handles simultaneous side-by-side entries, and test it in the pilot. This is where cheap counters lose their advertised accuracy. Related reading: how group entries distort counts.
- Staff exclusion. A counter that cannot distinguish staff patterns inflates visitor numbers and corrupts conversion metrics downstream.
- Accuracy verification. Do not accept the datasheet figure; verify against a manual count on your own doors using a written method: accuracy test methodology.
- Data path and ownership. Where do counts go, over what interface, and who owns the data? An on-site counter with a closed cloud can be a dead end for your BI stack.
- What sits behind the door count. An entrance count alone answers one question. If the project brief includes dwell, paths, or zone analytics, the counter needs to be part of a platform, not a standalone gadget.
Where Ariadne sits in this category
Ariadne measures this with Hybrid Fusion, its patented camera-free method. Time-of-Flight depth sensing counts every visitor at the entrances, capturing geometry rather than images, while patented phone signal sensing follows movement through the interior, detecting the signals a phone emits even in airplane mode, and tracks that movement to about one-metre precision. The sensor streams both feeds to Ariadne, where Hybrid Fusion combines them into one trajectory per visit and computes counts, dwell, and paths. The streams carry no identifier: no MAC address, no device ID, no biometric data, and no camera is involved. Identifiers are stored only when a visitor explicitly opts in, which keeps the method GDPR-friendly and outside biometric territory.
In practice that means the ToF unit at your entrance is one half of a measurement system: the door count is exact and camera-free, and the interior journey (which zones, how long, in what order) comes from the second sensing stream, fused in the platform. For a deployment conversation grounded in your own floor plan, book a demo.
# Program 3, Cluster 1 (Time-of-Flight) EN drafts: Part B (rows 205-208)
Status: EN drafts for review. Not pushed to CMS. No images, no DE yet.
Author: Govarthan.
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