Autumn usually means a change of colors. And in Japan it's not just the leaves. It is the time of year when the flashing lights of vending machines also go from green to red. In the first week of October, the vending machines that line the streets selling an endless range of drinks start twinkling different colors.

Under each displayed beverage, there is a little light indicating if it is in stock in the machine. Cold drinks have a green or sometimes blue flashing light. But in winter there are also rows of red flashing lights indicating you can get a canned coffee at a hand-warming temperature.

There are about 5.5 million vending machines in Japan, or one for every 25 people. Of course there are vending machines for all sorts of things apart from drinks. There are snack and cigarette machines, and other products from ice cream to hamburgers, rice to umbrellas, women's panty liners to DVDs. And, especially around major train stations, a wide variety of sex aids and condoms.

But it is the 3 million or so machines for drinks that are especially interesting. The average machine will have 18 to 20 different beverages such as bottled waters; flavored and specialty waters; carbonated drinks; juices; canned tea; and, the most prevalent, canned coffee. About one-third of all coffee consumed in Japan comes premade in a bottle, or more likely a can, from a vending machine. And on just about any block in any city, you will find two or more machines from different manufacturers lined up, a veritable smorgasboard of drinks on every roadside.

An increasing number of machines let you pay with a debit system built into your mobile phone. Some offer point-collection systems. And the machines act as minibillboards: Some have video built in, others talk back to you and some have digitized codes on their display panels that, when photographed by a mobile-phone camera, will automatically log the phone on to special promotion sites.

Great convenience if you are thirsty, but real pressure for marketers. For example, there is never one canned coffee in a machine but always five or more, and they are always adding flavors. So all year round there's a new drink available on the street. No wonder Japan is the home of constant innovation.