It is somewhat more difficult than that. The actual detonator has to be wired to the cell phone so that the electrical signal which would ring the phone triggers the detonator. I have no idea if the voltage is correct or if a more sophisticated circuit is necessary. Just putting the phone in a backpack full of explosives is not going to cause the explosives to go off when the phone rings.
Other precautions are necessary, which I will not go into on an open forum in the fervent hope that someone rigging one of these will ignore a precaution and have a work accident.
From reading the news accounts, the phones in this case were only used as timers. "But one more dud - the 14th bomb - went undetected for 12 hours until a mobile-phone alarm sounded amid luggage that had been taken from the bombed trains to a police station. The alarm was rigged to trigger the detonator but the bombers had mistakenly set it for 7:40pm instead of 7:40am, when the other devices exploded on the trains.
Had the detonator functioned, it would have blown up the police station. Instead police were able to examine the device for evidence and learn vital details of the methods and materials used to carry out the attacks."
Something smells about this part of the story. The 14th bomb should have gone off when the alarm on the phone activated. Either we are not getting the whole story or someone both miswired the device and set the alarm incorrectly.
While I wouldn't put two screwups one the same device beyond these guys, the odds that both mistakes would be made on the same bomb are very low. Especially when all 13 others worked as intended.
Consider the scenario where the bombers think this through and realize that all evidence will be collected in a central location. A second blast which destroys the evidence and kills a few investigators would make the investigation a lot more difficult.
For years, bombers have known about the tactic of placing two bombs, a small one to draw police and fire to the scene and then a larger one to attack the responders. It is not hard to envision an extension of this plan.
I think they've been watching BOTH Mona and Brandon. With her language skills and mideast connections and his military background and access to immigration stuff AND the fact that he's more concerned with Muslims than Americans, it makes a team.
Where are HER parents?? I see nothing to indicate that they are in the USA and no interviews with them????