7 July bombers bought special mobile phones
The 7/7 bombers borrowed techniques used by criminal gangs by using unregistered pay-as-you-go mobile phones, the inquests have been told.
A police expert said they used "tradecraft" counter-surveillance methods to keep the plot secret.
Det Sgt Mark Stuart said they bought "operational" phones while planning the bombings but kept them separate from their personal mobiles.
The inquests into the 52 deaths in 2005 are expected to last for months.
Det Sgt Stuart, a telecommunications expert, said that from May 2005 until the attacks Mohammad Sidique Khan, 30, Shehzad Tanweer, 22, and Hasib Hussain, 18, used four different operational phones each and Germaine Lindsay, 19, used three.
He said the mobiles belonging to Khan, Hussain and Lindsay were recovered from the bomb sites.
Det Sgt Stuart said they recovered data from Lindsay's phone, including text messages he sent and received.
The inquests have already heard that the four were hoping to launch the attack 24 hours earlier to coincide with the announcement of who was to host the 2012 Olympic Games.
But Khan postponed it, apparently because of complications his wife was having with her pregnancy, and texted Lindsay at 0435 on 6 July to say: "Havin major problem cant make time will ring ya when i got it sorted wait at home."
Lindsay, apparently angry, replied six minutes later: "No bullshit doctor! fix it!"
By the morning of 7 July the four bombers were ready.
Khan, Tanweer and Hussain drove from Leeds to Luton and met Lindsay, before all four headed into London.
Det Sgt Stuart said: "Apart from calls to each other, the only other calls made were to car hire companies, including the car hire company that was eventually used for the Nissan Micra left at Luton railway station."
One witness told the inquest how she almost bumped into Hussain on a busy Tube platform shortly before he killed himself and 13 others on a bus.
Janice Stephens said she almost walked into him as he sat on a bench at King's Cross station with his elbows on his knees at about 0840 BST.
She said she noticed him because he was sitting so far forward in the chair she had to change her path slightly as she came quickly around a corner.
"I remember thinking he had a jacket on. It was July so that was a bit unusual. He had a walking jacket on," she said.
About 20 minutes later, Hussain was captured on CCTV buying a 9 volt battery at a WH Smith shop in the station.
The footage, shown to the inquest, shows him rummaging around in his rucksack inside the store.
Hugo Keith QC said: "He spends a significant amount of time rooting around in a rucksack containing a highly unstable cooled explosive mixture."
Hussain is then seen going into a McDonalds for eight minutes, which Mr Keith suggests may be when he put the battery into the bomb.
At 0917 BST he is seen making a call on his mobile to Lindsay, who was dead by that time.
The last CCTV picture of Hussain shows him walking down Grays Inn Road at 0924 BST.
Police believe he boarded a 91 bus before the number 30 bus on which he detonated his bomb in Tavistock Square.
London Underground worker Fayaz Patel said that, in the aftermath of the bombs, poor radio coverage in the tunnels led to delays.
Mr Patel, who is now a Tube driver, told the coroner: "What you have got to bear in mind is people, members of staff and two BTP officers that were inside the tunnel, near the incident train, who could actually witness what was going on - their radios were not working.
"So the only way the message could be relayed to either myself or anyone in the control room was manually.
"They had to physically walk 100 yards to meet us back on the platform and relay the message manually. The radios on the platform were working but not those in the tunnel."
Mr Patel said some of his colleagues appeared reluctant to suggest over the radio that people might have been killed.
He said: "I was getting frustrated. We had customers coming out who were clearly injured but no-one to take them up the escalator or attend to them at platform level.
"I said on the radio: 'We are dealing with fatalities and can we get the emergency services to come down to platform level because the escalators are off'.'