Abstract: A friction pig 2 and system for monitoring one or more physical properties upstream and/or downstream of the friction pig 2 when in use in a pipe 1 is disclosed. The friction pig comprises at least one sensor 7 connected to the friction pig 2 for sensing and acquiring data related to one or more physical properties concerning the friction pig 2 or fluid upstream and/or downstream of the friction pig 2; means for receiving instructions from a remote control unit 12; means for carrying out instructions; and means for transmitting the acquired data to the remote control unit 12, thus enabling monitoring of one or more physical properties. Friction pigs preferably comprise friction plugs, for example high-friction plugs, for use in pipeline isolation. The invention is also described by a system comprising at least two friction pigs 2, 4 for measuring one or more physical properties when used in a pipe.