When there is a smell of gas in a house, the network operator and/or installer is alerted by the occupant. If the smell of gas is detectable by the nose, a highly explosive concentration of gas (4 % - 17 %) may already be present. The installer now undertakes a basic check of gas pipe parts for leak-tightness or to locate the leak. However, the gas leak detector must have an ATEX protection in this hazardous situation. The term ATEX comes from the French abbreviation for “ATmosphère Explosive”. This is a directive which includes the specification of which structural requirements must be met by measurement systems which have their own potential ignition sources and so could cause an explosion.