It is hoped that the "fixed speed indicator with automatic number plate recognition" will see drivers kill their speed on the Lower Mortlake Road in Richmond.
The scheme launched by London Safety Camera Partnership which includes Transport for London, the Metropolitan Police and London Councils (LSCP).
Number plates will not be recorded and speeding drivers will not be fined.
But it is hoped that the initiative will be a cheaper alternative to speed cameras or traffic calming measures.
A London Borough of Richmond spokesman said that early feedback showed that drivers were already cutting their speeds.
"We hope seeing their illegal driving highlighted will prove a strong deterrent and shame those who break the speed limit to ease off the accelerator," said Richmond's member for traffic, transport and parking David Trigg.
"We await the outcome of the trial with great anticipation."
Trigg added that if the trial in Richmond is successful, such devices could be introduced across London as part of a LSCP policy to promote "change of driver behaviour" rather than enforcement.
AA head of roads policy Paul Watters welcomed the new devices.
But he warned that it should be set at realistic levels and should not be used to enforce speed limits lower than those recommended by the Association of Chief Police Officers.
Watters added that the devices should be portable so that they could be used on lots of different roads to get the "maximum benefit".