COVID-19 pandemic has brought several limitations regarding physical distancing in order to reduce the interactions among large groups that could have prolonged close contact. For health reasons, such physical distancing requirements should be guaranteed in private and public spaces. In Spain, occupancy is restricted by law but in practice, certain spaces may become overcrowded. In practice there are law infringements and some places rely on movement estimations that may not be accurate. For instance, although it is known the number of passengers that enter a public transportation service, it is difficult to determine the actual occupancy of such a vehicle, since it is commonly unknown when and where the passengers descend. Despite existing a number counting systems, they are either prone to counting errors in overcrowded scenarios or require the active involvement of a person in the in/out process or even the user himself/herself (e.g., going through a lathe or tapping a card when entering or exiting a vehicle). This paper presents a novel IoT occupancy system that allows for estimating in real time the people occupancy level of public spaces like buildings, classrooms, businesses or moving transportation vehicles. The proposed system is based on autonomous wireless devices that do not need active actions from the passengers/users and require a minimum amount of infrastructure.

The system does not collect any personal information to ensure user privacy and includes a decentralized traceability subsystem based on blockchain, which guarantees the availability, security and immutability of the collected information in order to share it among smart city stakeholders (e.g., health authorities, insurance companies, mobility service providers, infrastructure operators, payment system providers, research institutions) to secure public safety and then deliver transparent decision-making based on data-driven analysis and planning.