Soon the detector will become silent, and you can walk away knowing it's still on guard. In some older units, the button only starts the warning sound, and does not tell you whether the detector circuit itself is working. Some newer detectors have more refined test systems that simulate the presence of smoke in the chamber. These don't need to be tested with real smoke. Check the package or instructions of your detector to see if it has this feature.
Some authorities suggest testing every two weeks.
This should not reduce battery life significantly. Testing more often than this may shorten your battery's life. At Once Batteries will last approximately one year. Have a new battery on hand always. Replacement lamps for photoelectric detectors also should be kept on hand so no delay occurs in restoring their function.