- An app driven by a SIM card is installed in the bin
- An infra-red sensor in the bin works out how full it is
- Messages are then sent by text to Westminster City Council
More top news
Andreea Cristea's partner Andrei Burnaz was due to propose to her on the day she was pushed by a car into the river Thames.
Owen Lambert, 18, and his friends were on a university trip to Parliament when they were hit by the Westminster attacker's speeding car.
As the investigation into Khalid Masood continues, former acquaintances tell of violent incidents in the murderer's past.