The detector should be located in an area where you expect that gas leakage can begin to cause damage or injury, but not trigger a false alarm during the normal operation of the gas equipment (e.g gas stove). We cannot give an exact distance from the gas source. It should be tested on the place to find the best location. Usually it is quite near the gas source. Let's imagine that a gas leak has occurred, but the sensor is located 20 feet away from gas equipment and air circulation from, say, a window, blows the gas in the opposite direction from the sensor. In this instance you may never get an alert. We would recommend that you test on the place. The length of the cable is 16 feet (5 meters). You can extend it, but only affects the distance between the sensor and the iSocket unit, not between the sensor and the gas source. For most installations 16 feet (5 meters) should be sufficient.