Device Activity Tracker – Infers phone activity via WhatsApp timing side-channels

Summary: Device Activity Tracker is an open-source proof-of-concept that infers a phone’s activity state by measuring round-trip times of silent “ghost” reactions on WhatsApp and Signal. It detects screen status and network conditions without sending visible messages or triggering notifications.

What it does

It sends invalid reactions to specific message IDs and measures delivery receipt timing to estimate if a phone is active, on mobile data, in standby, or offline.

Who it's for

Researchers, security teams, and journalists interested in studying messaging app side-channel leaks.

Why it matters

It exposes timing-based side-channels that reveal device activity without user awareness, highlighting privacy risks in messaging platforms.