Rong, sorry but not quite right, we will acknowledge the code and deactivate the alarm on the console ( if fitted), we then follow a checklist of items and it is the Airline company's call as to the level of credibility for a bomb threat and the Department of Transport / dept of defence / CASA / airline /ATC who determine if the 7500 is to be treated as such if that is the only indicator, accidental activation of distress is common on some aircraft types where it can be activated by a hidden foot activated switch. It is very rare and usually in error that a 7500 gets activated. The 7700 is slightly more common and the 7600 is probably a daily occurrence across the country. We strongly recommend mobile phone contact as a measure to be considered in a radio failure, be conversant with both AIP AND ERSA entries for the airport / airspace concerned and remember, AVIATE, navigate and then communicate. The first two will keep you alive and the last one will aid you in getting some help and letting others know to be aware. Be aware there are significant fines for intentional misuse of the distress codes, also, don't rely on them being received, there was in incident 5 years ago in outback NSW, a pilot had a partial power failure of one power bus, he lost VHF radio and one transponder, the other transponder he thought was working but it wasn't, he did the right thing and dialled up 7600 and flew the last 2 1/5 hours without doing anything else. He landed at a busy airport in the middle of a large military exercise , when confronted on the ground, he was angry no one new he had the failure, this airport and the altitude and route he flew were out of radar coverage, the 2nd transponder didn't work and he didn't / hadn't read ERSA / AIP SUP / NOTAM to know what to do and what was available to use. He landed against light signals from the Tower, didn't use his HF radio that did still work and didn't use his mobile phone when he was within range. Like most things in aviation, even down at the lower end of RAA, take the time to think the problem through, know your equipment and the airspace you are in, not a radar tower then 7600 or any other code may well be useless, don't think that you have done all that is required, you may still KILL YOURSELF. The saying goes, there is ALWAYS more than one way to skin a cat..