Not sure I like the name "Horn Bike" but I like the idea of this passive and inexpensive iPhone bike speaker. Sure you could wear earbuds, but you might end up as a hood ornament on a Prius.
The Horn Bike is similar to other passive speakers we have seen in the past but comes with a velcro system for attaching your iPhone 4 to your bikes handlebars. This clever iPhone 4 and iPhone 4S passive bike speaker will boost your volume level by about 13 decibels without any additional electricity usage. Yours for $29.95 here.