Phase-sensitive or ”lock-in” amplifier is a device which singles out wanted signal from a noisy background using a method of lock-in detection which then allows its measurement. These types of devices are a result of harmonious operation of large number of components which makes them very expensive. Therefore, in this thesis we are dealing with one alternative low-cost variant of lock-in amplifier and aim is to describe it and compare it to a standard commercial variant of PARC model 5210 dual phase lock-in amplifier. After the description of their functioning, frequency range of the low-cost variant is tested and then both variants are applied on a simple circuit. By comparing obtained results, we conclude that low-cost lock-in amplifier is definitely applicable and capable of singling out a signal of amplitude in the range of 10^−4 V in a noisy environment shown with picture 5.7. Functioning of a low-cost lock-in amplifier on high frequency is shown on pictures 5.1 and 5.2 while on the low frequency it is shown with pictures 5.3 and 5.4. Frequency range of a low-cost lock-in amplifier is around 10 Hz − 100 kHz which at least in this segment, makes it comparable with model 5210 dual phase lock-in amplifier for which the frequency range is 0.5 Hz - 120 kHz [9].