The problem of detecting signals in the presence of interference arises in various areas of radio engineering and is solved by using the selected indicators of the signal presence that are compared with a specified threshold. In this paper, an algorithm for detecting a discrete signal is proposed, with the decision threshold that determines the false alarm probability and does not depend on the noise level, while the missing probability depends only on the signal-to-noise ratio. The decision is made according to the number of exceedings of the threshold level by the modulus of the logarithm of the ratio of the amplitudes of the received and previous symbols in a sampling of a given size. For the false alarm and missing probabilities, the theoretical expressions are obtained. Statistical simulation of the detector for the case of a phase shift keyed signal is carried out. It is proven that the number of false alarms is not influenced by the noise parameters while the introduced detector provides high noise immunity and efficiency.