Mobile phone detectors are to be used by police to find drivers using devices at the wheel.
The Thames Valley and Hampshire forces are rolling out the technology to show when motorists are using their phones.
A sign will flash at the driver telling them to stop using their mobile – but the detectors cannot tell if it is a driver or passenger using the phone.
The mother of Aimee Goldsmith, 11, killed by a driver using a phone, said it was a “step in the right direction”.
The technology will not be used as an “enforcement tool”, the forces said, but was instead aimed at educating motorists and identifying offending “hotspots”.
Kate Goldsmith’s daughter was one of four people killed in the crash when lorry driver Tomasz Kroker was using his phone at the wheel in 2016.
She said Aimee’s death was “completely avoidable”.
“Most mothers look forward to planning their daughter’s weddings. I had to plan Aimee’s funeral,” she said.
Ms Goldsmith said she had confronted drivers using their phones behind the wheel since her daughter’s death.
“I have stopped a few people and said, ‘you’re using a mobile phone – it’s actually a driver like you that killed my daughter’,” she said.
She said the detectors were “not a perfect solution” to convict offenders but were “a step in the direction”.
Kroker killed Aimee, her stepbrothers Ethan Houghton, 13, Joshua, 11, and their mother Tracy, 45, when he ploughed into stationary traffic at 50mph on 10 August 2016.
He was jailed for 10 years after admitting four counts of causing death by dangerous driving and footage showed him on his phone at the moment of impact.
A judge said the 30-year-old’s attention had been so poor he “might as well have had his eyes closed” before the crash on the A34 near Newbury.
