An apparatus in an example comprises a manipulator, a force sensor, a signal modulator, and a visual indicator. The manipulator is employed by a user. The force sensor determines a force signal from a force applied by the manipulator on a part of an environment of the user. The signal modulator is adjustable by the user to select a switch point for the visual indicator based on relative fragility of the part of the environment. The signal modulator employs the force signal and the switch point to control the visual indicator for the user.