In Japan, U.S. military personnel and their families have been warned not to use a number of wireless devices (baby monitors, cordless phones and so on), because they use frequencies too close to those allocated to cell phone service in Japan. This is not a new problem. Five years ago, garage door openers were sudden being activated by military radios in the United States. That was because, for over half a century, one of the radio frequencies reserved for military use in the United States (380-400 megahertz band). But starting in the 1980s, manufacturers of garage door openers were allowed to use the 390 megahertz frequency, because the openers were very short range (low power) and unlikely to interfere with military radios (or vice versa). But a new generation of military radios has changed all that, by sending out powerful 390 megahertz signals.
The problem was first noted five years ago, as new military radios, using the 390 megahertz frequency, were installed on military bases. Now, over 125 bases are using the new radio system. While the Department of Defense believed that the new radios only made garage door remote control systems inoperable, thousands of users reported seeing garage doors open and close by themselves. Since the garage door system manufacturers were using the 390 megahertz frequency unofficially (but with the knowledge of the government), they had to change their equipment to use another frequency. Over 50 million garage door systems (those within 80 kilometers of a military base), were involved.
There are increasing problems like this, as more wireless equipment comes into use, and the military makes more use of frequencies they have long owned but not really worked hard. It's not a new problem, and was first noted on a large scale during the 1991 Gulf War. Here, there was a large concentration of military equipment form all the American military services, and foreign armed forces as well. There were several unexpected incidents where frequencies collided in unexpected ways. There was some of this again in Iraq after 2003. There will be more conflicts like this, and some of it will be in combat, with deadly results.