Isolating sick patients, tracing their contacts and placing them into quarantine is a strategy used by generations of public health physicians in their fight against infectious disease. As coronavirus lockdowns around the world start to ease, new systems based on this strategy are being rolled out to prevent a resurgence of the pandemic. If these systems do not consider the behavioural issues posed by symptom reporting and quarantine, they will struggle to meet their goals. The goals of this commentary are to outline the key behavioural issues that a test, trace and isolate system for the management of COVID-19 will face, and to suggest specific ways that system design can address these. In this paper, we highlight five areas in which these behavioural issues should be taken into account, structured to follow the steps of the test, trace and isolate process: development of symptoms; reporting of symptoms; isolation; reporting of contacts; and quarantining contacts. The issues we highlight largely apply regardless of the modality of system, be it via an app, website or in-person consultation.