This master thesis revolves around the development of a personal alarm device for lone workers. A lone worker is somebody who is regularly isolated from their colleagues, without direct supervision. This includes people who often work in isolation, like electricians and warehouse employees. But a worker does not need to be alone in order to be considered a ‘lone worker’. A nurse who is regularly alone with their patients is also considered a lone worker, since there are no colleagues in their direct vicinity. Compared to regular workers lone workers are more vulnerable to (the consequences of) aggression, accidents and illnesses. The main reason for that fact is that they inherently face a number of factors that create both physical and figurative distance between them and potential sources of help. This means that it will take longer for potential sources of help to notice that anything is wrong at all or to reach the lone worker’s location. If a nurse is attacked by an aggressive patient while they are alone together in a room, their colleagues might be physically near but the figurative distance between them can be huge. The thesis discusses various subjects related to lone workers and their safety, including: aggression, accidents & illness, privacy. The final product is a wearable personal alarm device that is connected to a smartphone. It allows lone workers to call for help whenever they need to. It aims to improve both the objective and the perceived safety of lone workers. The device is connected to a network of lone workers within an organisation, and can be used to send and receive alarm pulses that any nearby lone worker will feel through haptic feedback. The alarm pulses contain information on the urgency of the alarm pulse and the identity and location of the alarm maker. The alarm always escalates to the best available source of help. If a colleague is in the vicinity of the alarm maker, the alarm will escalate to them, allowing them to help each other out. If there are no colleagues nearby the alarm escalates to an Alarm Receiving Centre (ARC), run by a third party security company. This ARC is specialised in responding to incidents remotely, and will dispatch the most appropriate source of help.