A novel approach to fully automating the Timed Up & Go (TUG) assessment test in professional and domestic environments is presented. The approach, called aTUG, is based on the usage of ambient sensor technologies i.e. two light barriers, four force sensors, and a laser range scanner built into a single apparatus i.e. a chair. aTUG supports execution and documentation of traditional TUG and enhanced component-based TUG. aTUG defines five components: Standing up, walking there, turning, walking back, and sitting down. Algorithms for detection of those components and for computation of their duration and the duration of the whole TUG are presented. An experiment with five elderly patients aged 74-91 years, four female, one male, most multi-morbid has been conducted in a residential care facility in Oldenburg, Germany. Results of the experiment show that aTUG can reliably and precisely measure total duration of TUG and durations of the single components with mean error of only 0.05 seconds and mean standard deviation of 0.59 seconds using especially its force and range measurements. German patent is pending for the presented approach.