This work addresses the problem of detecting devices which are stealthily attached to the computer for logging keystrokes from keyboards. These devices are known as hardware keyloggers (HKL). When an HKL is attached to the keyboard, certain electrical characteristics of the keyboard signal are altered. Based on these characteristics (features), differences have been identified in an accurate assertion was made about the presence of HKL. The characteristics from which the differences were obtained were used to make distributions and compared with distance-measuring methods. An experiment was done to collect data from a number of keyboards and form two distributions (training and test) to perform the comparison. It was possible to detect the presence of HKL in the keyboard with a minimum of 4 to 100 keystrokes. For justifying the stability of the features, the temperature of the surroundings was obtained and the dependence of the features on temperature was obtained. Also, an experiment was done to see whether the keyboards were uniquely affected by the HKLs. This was done without using any training data, i.e., the distribution of features which was used did not come from a known state of the system (either with HKL or not with HKL).