Distributed acoustic sensing (DAS) has recently drawn attention in perimeter intrusion detection (PID) systems. Fibre optics provide considerable benefits compared to other systems because of its specific qualities, such as compact size, working capability in difficult conditions, resistant properties to electromagnetic interference, and competitive pricing. Standard differential and normalised differential technique were explored together with wavelet denoising approach to improve the Signal-to-Noise Ratio of detectable signal by 1.59 dB. The system is able to detect a person stepping on the fibre at spatial resolution of 8 meter.