Senior citizens and patients recovering from surgery or using strong medications with severe side effects tend to fall unexpectedly. The consequences of such an uncontrolled fall could be worse than the original malady, especially when there is no communication with the care-takers. We describe a fall-detector device capable of distinguishing falls from normal daily activities. Based on three-axis accelerometer and advanced data processing, the microcontroller emits an alarm requesting help in the case of a physical fall. We design and construct the fall-detector prototype for either inside or outside use. In order to determine the device performance, fifty instances of each fall event have been evaluated; all of them detected as fall event. In the case of daily activities, the only movement that produces an alarm is the transition from standing up to lying in 5% of the occurrences.