A method of monitoring a reservoir comprising setting at least one barrier in a well separating it into upper and lower isolated sections. A perforating gun or other perforating device is provided in the lower isolated section, along with a control mechanism, wireless communication device and a pressure sensor. After the barrier is set, the perforating gun is activated in order to create at least one perforation between the well and a surrounding reservoir. The well, or part of it, is suspended or abandoned but the pressure is still monitored and a wireless, preferably acoustic or electromagnetic, data signal is transmitted from the lower isolated section to above the barrier. Data from the suspended/abandoned part of the well may be used to infer characteristics of the reservoir so that it may be exploited more appropriately especially through another well.