One of the most important properties of brittle materials is static fatigue. To measure this property, the specimen is loaded under constant stress and the fracture occurs after an elapsed period of time. The scatter in this time is large, and to obtain a good statistical representation it is necessary to test a large number of samples (over 20). Due to this scatter, the time for some of the tests could be large, and a period of several months might be necessary to test all the samples. In this article we describe an automatic optical detector for fracture that was employed to study the static fatigue of transparent materials. The main advantages of this instrument are (i) automatic registration of fracture for long periods of time, (ii) application on bending tests (this reduces the testing space) of low strength materials, and (iii) the cost is low and the number of samples can be increased with practically no increase in cost.