Google is stepping up its Glass promotional efforts, by offering free demonstrations of the wearable device. The search company is sending e-mails to potential users interested in the headwear, inviting them to to try it out, supervised by a Google employee, at one of the Glass service centers in Los Angeles, New York, and San Francisco. The e-mail received by CNET advises that the demonstration sessions with the “Glass Guide” are by appointment only. It also states the prospective user can also bring along a guest for the trial, though it is stipulated they must be over the age of 13. From the description on the support page, it appears that it will be an indoor-only test, with users being required to hand back test units after they have been tried out.