A suction-adhered device includes a main body, suction cup units, and suction power detection units. The main body is provided with chambers. Each of the suction cup units includes a suction cup received in the chamber, and a safety lever projected from the upper side of the main body and movably connected to the suction cup with an elastic element mounted between them. Each of the suction power detection units includes a probe received in a long hole near the chamber to partially project from the long hole, and an indicating member visible via a window formed on a top of the main body above the long hole. When the suction cup is loosened from a mounting surface, the indicating member is turned by an elastic element to show a warning indicating zone thereof, so that a user may be timely warned to re-mount the main body.