Pagers have been as synonymous with the medical community as scrubs, stethoscopes and lab coats.
But cell phones -- their electronic cousins -- have historically been persona non grata with the hospital set.
Electromagnetic interference from cell phones and other transmitting communication devices was thought to affect the performance of medical equipment.
Now, as technology improves, more hospitals in the United States and the United Kingdom are relaxing and lifting long-standing bans on cell phones.
But though the door is unlocked, it's not swinging all the way open. Experts caution that though the interference risks are low, they are still significant enough to warrant some limitations on cell phone use in health-care facilities.
In 2007, researchers at the Rochester, Minn.-based Mayo Clinic published one of the first reports to dispel the widespread notion that cell phones negatively affect patient care equipment.
Previous tests in 1997 and 2000 found that cell phones, especially older analog phones, could interfere with heart monitoring equipment and other sensitive medical instruments. In one case, a cell phone signal caused a ventilator to shut off.
But the most recent tests, on medical equipment better shielded against interference from wireless communication devices, showed researchers that the threat had dimmed.
In five months, the researchers performed 300 tests in patient rooms and determined that the normal use of cell phones resulted in no noticeable interference with medical equipment.
"When we watched the monitors, we didn't see anything that seemed clinically significant," Jeff Tri, one of the authors of the cell phone study, told ABCNews.com.
Those results -- combined with patient requests for cell phone use and the difficulty in enforcing a total ban -- not only persuaded the hospital to change its policy, but prompted it to encourage other hospitals to do the same.
"We said we don't think the incidence of interference is great enough to warrant the policy staying where it is," Tri said, adding that the two exceptions to the policy were the surgery and pediatric and neonatal units, as studying those areas would have required a different process.
Noting the receding threat, earlier this year, health officials in the United Kingdom gave hospitals the go-ahead to relax their cell phone restrictions.
"Close support and comfort from loved ones when you are in hospital is essential. Mobile phones are commonplace in everyday life and people have told us they'd like to be able to use their phones in hospital to keep in touch," Ben Bradshaw, the U.K. health minister, said upon issuing the guidance.
But health-care technology experts continue to caution that cell phones are not entirely free of risk.
"We would be concerned that the [U.K.] decision creates an impression that cell phone interference with medical equipment doesn't exist. And though it's rare, interference events do occur," said James Keller, vice president of health technology evaluation and safety for the ECRI Institute. ECRI is a nonprofit organization that tests medical devices and provides guidance to hospitals.
When the Mayo Clinic study emerged, ECRI issued a similar statement, emphasizing that Mayo's research was not comprehensive enough to prompt a change to its cell phone position.
Art Augustine, ECRI's senior project engineer, told ABCNews.com that although medical equipment is increasingly protected from electromagnetic radiation with metallic coatings and more secure seals around the seams of devices, interference issues persist.
Ventilators, anesthesia machines, life-support equipment and infusion pumps delivering critical drugs are all vulnerable to interference from cell phones that are one meter or less away, he said.
"We advocate a partial ban in critical-care areas," he said. Doctors, nurses and other clinicians are advised to turn cell phones off when they approach patients dependent on medical equipment.
In 2005, an ECRI survey found that 48 percent of 122 participating hospitals banned cell phones from critical-care areas. Twenty-nine percent banned cell phones from all patient care areas, 12 percent had no ban and 11 percent had a complete ban.
Although the survey is a few years old, Augustine estimated that the results had not changed significantly.
Like the Mayo Clinic, Ohio's Cleveland Clinic also subjected its equipment to a 10-month-long series of cell phone interference tests that ended in 2007. But its research led the hospital to a different conclusion.
Although the research prompted the hospital to relax its total cell phone ban, the hospital decided to maintain a partial ban that prohibits cell phone use in any patient care area.
The hospital tested 12 different cell phones, including BlackBerries, that were compatible with several different carriers.
And it discovered that although it didn't happen frequently, in some cases the cell phones detracted from the performance of key medical equipment.
In one instance, a cell phone signal interfered with a telemetry unit's ability to detect a patient's heart rate. In another, the signal changed an alarm level on heart rate monitor.
"You can say 99 times out 100, it's not going to cause an issue. But do you want to be the one patient when it does cause an issue?" Paul Miklovich, administrative director of patient support services, asked ABCNews.com.
Because the clinic wanted to be sensitive to patients' and visitors' desire to stay in touch with friends and family while at the hospital, it eased up on the total ban. But, Miklovich said, its research could only support a limited-use approach.
Miklovich said his clinic constantly reviews the research and regularly submits medical equipment to batteries of tests. But, he acknowledges that not all hospitals have the same resources and must establish policies that match their different needs.
Hospitals with older equipment, for example, might need stricter policies.
"A lot of hospitals don't have the resources to do that testing," Miklovich said. "Each hospital has to judge what they can do."