The Social Internet of Things (SIoT) builds up the communication architecture of state-of-the-art smart cities. Invulnerable IoT devices play a pivotal role in successfully deploying smart city services. The proposed model for Quality of Life (QoL) signifies the careful coordination between the smart APIs and the underlying devices, which are vulnerable to heavy traffic, security attacks and technical snags. Successful deployment of smart-city applications requires a proper quantification of the invulnerability of the IoT devices against these adversaries. The empirical model, QoL, presents a technology-enabled quantitative measure to estimate the sustainability of the smart city with the help of device parameters.