Our technology
Passive Wi-Fi
The advantage of passive Wi-Fi
Since the advent of “smartphones”, beginning with iOS and Android, phones have spontaneously broadcast Wi-Fi probes for purposes of geolocation. Apple’s iOS phones also spontaneously broadcast BLE probes (known as “advertisements”) but virtually no Android phones do, limiting measurement accuracy using BLE. To learn more about the advantages and limitations of BLE visit this page.
| Technology | Wi-Fi | Bluetooth Low Energy (BLE) |
|---|---|---|
| Share of smartphones that broadcast | 100% of smartphones probe | 100% of iOS smartphones advertise, but very few Android smartphones advertise |
| Maximum detection distance (can be reduced through calibration) | Up to 300 feet (100 meters) with standard antennas. | Up to 30 feet (10 meters) with standard antennas |
| Median inter-arrival time of smartphone broadcasts | 32 seconds median | 1.2 seconds median (for iOS only) |
| Lifetime of randomized smartphone addresses | 8 hours median (for local MAC addresses) | 4.1 minutes median (for iOS only) |
| Chaining of broadcasts across address rotations | Chaining not highly relevant due to long local MAC address lifetime Long local MAC address lifetime makes in-store shopper journey easy | Chaining possible, but technique is fragile: (1) best in low occupancy zones, (2) requires continuous sensor coverage and (3) Apple payloads are proprietary and can be obfuscated (to prevent chaining) in any future OS release |
| Utility based on people present | Excellent accuracy in zones with long dwell times (e.g. slow-moving phones, large zones) Poorer measurement accuracy in zones with short dwell time (e.g. fast-moving phones, small zones) | Excellent measurement of dwell times below 1 or 2 minutes (e.g. fast-moving phones, small zones) Poorer measurement accuracy in very low occupancy environments (e.g. small panels). Non-iOS smartphones are not detected. |
Most phones broadcast these probes even when Wi-Fi is disabled (meaning they cannot connect to an access point) or when in airplane mode. This is true whether or not phones are connected to a Wi-Fi access point. Mobile phones identify available networks by broadcasting probes that say “I am here; is an access point out there?”. The phone identifies itself by broadcasting its MAC address.
These probes prompt access points (e.g. including most routers) to respond with their SSID (Service Set Identifier) and whether or not that access point requires a password. A mobile phone might broadcast a 12-hexadecimal-character (6-byte) MAC address (e.g. 4A:78:1E:95:FA:23) and in response learn that three access points are within range.
BlueZoo sensors passively listen for Wi-Fi probes. These sensors can be BlueZoo’s own hardware devices or can be third-party hardware running BlueZoo firmware. Our sensors listen for phones in a “detection zone”. The shape of the detection zone (either spherical or conical) is defined by the “pattern” of the antenna employed. The “size” of the detection zone is determined by the minimum signal power of the probes received from the smartphone. The closer the smartphones are to our sensor’s antenna, the higher their signal power.
Based on the trillions of probes heard by our sensors worldwide, our cloud systems are able to calculate a real time count of smartphones in the detection zone, along with length of time (i.e. dwell time) a phone remains in a zone, among other details. We don’t know who owns the phone or why the owner has visited, but we often know if they’ve been here before and sometimes where they have come from.
Wi-Fi has evolved enormously since it was first introduced in the 1990s. Originally, all MAC addresses were “Global” addresses consisting of a 3-byte Organizationally Unique Identifier (OUI) that identified the company making the equipment, and a 3-byte serial number. Starting in 2014, after revelations by Edward Snowden about the tracking of mobile phones using Wi-Fi, Apple iPhones began probing with “Local” (i.e. randomized) MAC addresses. Google’s Android phones adopted “Local” MAC addresses in 2017. Most new smartphones probe with Local MAC addresses by default, though some new phones do not provide these capabilities and others don’t elect to use them.
Wi-Fi is best suited for:
- Large-area audience measurement
- Direct measurement of both Android and iOS smartphones
- Unique visitor recurrence measurement
- In-store shopper journey mapping
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