When considering the use of new surveillance technology, a legal analysis requires determining whether its proposed applications constitute a "search" within the meaning of the fourth amendment. It also requires testing to establish that the device does not produce a high percentage of false positive results. Operator proficiency is also an issue. A poorly trained operator can make the device less reliable and also risk having the evidence excluded from use in court. The more the surveillance focuses on a particular subject and has a narrow goal, the less likely it is to cross legal boundaries. When the surveillance acts as a "dragnet" and large masses of people are involved, it is more vulnerable to fourth amendment violations. Less-than-lethal technologies must also be subjected to legal tests, because they may pose a risk of public harm; for example, the Long Range Acoustic Device (LRAD) can be used for crowd control and as a combatant deterrent; however, at close range it can permanently damage hearing. At intermediate ranges and for only a few seconds, the sound can be painful but does not cause permanent damage. Surveillance, jamming, and less-lethal technologies that rely on radio frequencies are not only constrained by privacy and excessive force issues; their use can be limited because they emit electromagnetic radiation in radio frequency bands that can interfere with many types of communications. Jamming of frequencies is usually illegal, and radio frequency transmissions should not obstruct essential communication.