Passengers' Safety Matters: Experiences of Deploying a Large-Scale Indoor Delivery Monitoring System

Delivering goods to many indoor stores poses significant safety issues, as heavy, high-stacked packages carried on delivery trolleys may fall and hurt passersby. This paper reports our experiences of developing and operating DeMo, a practical system for real-time monitoring of indoor delivery. DeMo attaches sensors to trolleys and analyzes the Inertial Measurement Unit (IMU) and Bluetooth Low Energy (BLE) readings to detect delivery violations such as speeding and using non-designated delivery paths. Differing from typical indoor localization applications, DeMo overcomes unique challenges such as unique sensor placement and complex electromagnetic characteristics underground. In particular, DeMo adapts the classical logarithmic radio signal model to support fingerprint-free localization, drastically lowering the deployment and maintenance cost. DeMo has been operating since May 2020, covering more than 200 shops with 42,248 deliveries (3521.4 km) across 12 subway stations in Hong Kong. DeMo's 3-year operation witnessed a significant violation rate drop, from 19% (May 2020) to 2.7% (Mar 2023).