A trigger circuit (10) comprises a switch member (SW1) connected in series with a high-ohmic resistive element (R1), the junction between the switch member and the resistor element being connected via a capacitor (C1) to the input of a circuit (20) to be triggered. The circuit (20) operates a light-emitting source (130, FIG. 3). The switch (SW1) can be a user-operated switch, a tilt switch (100, FIG. 2) or can be a comparator (124) responsive to an external factor e.g. incoming vibrations.