Multimorbidity and age-physiological functional restrictions can lead to frailty and a loss of a self-determined life in elderly patients. The Timed Up-and-Go test (TUG) is a sensitive and specific measure of frailty and has also many other areas of application, for example in chronic diseases. Besides the measurement of the complete TUG time, the analysis of subtasks may also reveal important information about particular aspects of the health status of test subjects. We developed an ultrasonic-based device for performing the TUG automatically, which can be attached to the backrest of a chair. This device provides the total TUG time as well as the displacement-time data for all included subtasks. To prepare for its use in clinical studies, we performed a field test at a geriatric center. The goal was to confirm feasibility, i.e., to assess its application in real patients. Despite some improvement potential revealed by the field test, the concept turned out to be an appropriate method for monitoring the TUG time and its subtasks.