You walk past and something shifts. Particles drift toward you — clustering, brightening — then slowly disperse as you move on. At first it reads as ambient light. Then you notice it’s tracking you and responding to you.
Ephemeral Presence captures the ambient Bluetooth signals broadcast by phones and devices moving through Toronto’s public spaces — signals that are always there, never visible. Custom detection hardware reads this activity in real time, translating each detected device into a particle in a responsive light field. Proximity determines brightness; movement shapes behavior; collective presence builds complexity that no single person generates alone.
The work requires nothing beyond being there. But the closer you look, the more the field reveals — not just your own signal, but the accumulated digital traces of everyone nearby, drifting together in a space most people walk through without a second thought.
The installation used passive Bluetooth Low Energy (BLE) scanning — the same wireless technology that connects your phone to AirPods, Apple Watch, and smart devices. A scanner near the artwork detected every BLE-active device that came within range over the 12-hour overnight event, without collecting any personal information.
Each detected device is counted once as a unique appearance. The engaged audience figure combines two groups: people who had sustained near-field contact (≥2 min with strong signal) and interaction candidates who engaged briefly but meaningfully (≥1 min). Because the scanner sat ~25–30 ft behind a window, signal attenuation means some clearly engaged visitors fall just below the strictest threshold — combining both groups gives the most complete picture. All zone thresholds are calculated using the Bluetooth SIG free-space path loss specification.
Not everyone carries a BLE-active device. Research on exhibition audiences (ResearchGate, Panda Security, Uniti) suggests roughly 20–30% of people at an art event may have Bluetooth turned off — with younger, tech-engaged audiences like those at Nuit Blanche skewing toward the lower end. Some attendees also carry multiple devices (phone + watch + earbuds) that each register separately, partially offsetting that gap.
Applying this correction to the directly-measured BLE attendance estimate of ~2,100–2,700 people gives an adjusted total of ~2,700–3,800 people — consistent with a strong overnight showing for an installation in the Fort York area under the Gardiner Expressway.