The introduction of eTicket readers will result in faster and more convenient train travel, say rail bosses.
Passengers using the Govia Thameslink Railway (GTR) network can now skip standing in line for a paper ticket.
Barcode readers have been added to all ticket gates at Southern and Thameslink-managed stations.
They will allow commuters to scan eTickets from their smartphones or those printed out from an email.
GTR customer services director, Jenny Saunders said: “Barcode eTickets are quick to buy online and convenient to use. They’ll make everyone’s journey simpler.”
The electronic tickets can be purchased instantly through train firms' On Track App or websites with no booking fee.
They are ideal for advanced singles, peak and off-peak singles and return fares.
The roll-out of eTickets means some passengers can avoid problems with accessing the traditional paper version.
In January, commuters at Greenhithe faced rush-hour delays after the station’s only ticket machine was out of order for four running days.
Last year, rail users at Rochester station called for more machines and a ticketless solution amid similar commuter chaos.
Meanwhile, a proposal to close railway station ticket offices was scrapped in October after a huge backlash.
Disability rights campaigner Sue Groves joined nationwide pressure groups to protest against the idea on equality grounds saying it discriminated against blind or partially-sighted, elderly and disabled people.