In general, all wireless phones have some weaknesses as emergency devices. Although the F.C.C. has ruled that 911 should become the universal emergency number, not all areas of the United States have the service, so calls in some areas might go unanswered. And as anyone with a wireless phone knows, you cannot always get a signal -- even in the middle of a large city. Also, wireless phone networks are not available in 20 to 30 percent of the United States, although most of those areas are unpopulated.

There may be other disadvantages to using uninitialized cell phones for 911 calls. For example, signals from old phones that operate on an analog network would not be picked up by a digital-only service like Sprint. In some areas, that could reduce the chance of a message getting through.

SecureAlert says its phone, which is priced at $199, has advantages over using an old wireless phone. ''We have powered it with AAA batteries, which will give you use for well over a year without charging and recharging,'' said Brian Boling, a partner in SecureAlert L.L.C., which licenses the Magnavox brand name. The phone also has a single, large 911 button, making it easy to use. And it has a siren to attract help.

Used wireless phones can be purchased from Web auction sites for less than $10, and even though uninitialized phones have drawbacks, they are not far worse than regular cell phones, and they are certainly better than nothing.