The scanners will be used in all Waltham Forest schools
Knife arches are to be introduced in all secondary schools in an east London borough so that pupils can be regularly screened for weapons.
From Wednesday, all pupils at Waltham Forest's 22 secondary schools are to be screened about once a term.
The council launched the scheme after requests from young people who said they wanted to feel safe in schools.
Teachers, students, police and councillors denied the presence of the arches would criminalise young people.
Chris Robbins, from Waltham Forest council, said: "There's no doubt that there is an issue of knife and weapon crime in London and it would be foolish to ignore that."
He added that the initiative would tackle serious crime as part of a larger educational programme which involved the police talking to students about the danger of weapons.
The scheme was launched at Lammas School and Sports College in Leyton, east London.
Marco Santo, 12, said he was "a bit nervous before walking through the arches" but that it "wasn't that bad".
Mischa Haynes, also 12, said: "It makes you feel safe in school and it's a place where you should feel safe."
So far 15 schools and 12,000 pupils in the borough have undertaken weapons screening as part of the first phase.
No weapons were found.
All the borough's schools have signed up to the Weapons in Schools Protocol.