Toyota is to sell an optional noise-generator for its Japanese-model Prius hybrid, the company confirmed this week.

Buyers in Japan will be able to add the speaker system, which makes an artificial noise to make the near-silent vehicle obvious to pedestrians, for 12,600 yen (€117).

The sound is "aimed to alert but not annoy," said Toyota, and will be audible at a rising and falling pitch at speeds of up to 25 km/h when the vehicle is in all-electric mode.

It goes on sale on August 30 but will only be available on Japanese models at first, although Toyota is considering making it available in other markets, reported US motoring blog Inside Line.

The inclusion of the system as an optional extra and the possibility to turn it off with a switch is likely to draw criticism from safety organizations and groups representing blind people, for whom electric vehicles (and hybrids in all-electric mode) can be dangerous.

In June, the US National Federation of the Blind criticized the "Approaching Vehicle Sound for Pedestrians" featured on the Nissan LEAF, warning that the option to disable the system could endanger pedestrians.

Reports suggest that the Chevrolet Volt will take a different approach, including a driver-activated warning sound which is distinct from the horn but operated in a similar way.

Hear the system in operation:

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