The invention relates to providing detection of an exposure to a physical or chemical phenomenon and revealing information as a response to the exposure. A microfluidic device (20) comprises a microchannel (22) filled at least partly with at least one substance and a conductor (29) providing an intersection area (23a-23d) with the microchannel (22). As a result of exposure to the physical or chemical phenomenon directed to the microchannel (22) or to the substance in the microchannel (22) the microfluidic device (20) is arranged to control electromagnetic characteristic of the conductor (29) in the intersection area (23a-23d). An indicator device (45) comprises the microfluidic device (20) that is connected to means for indicating (40) to indicate the exposure to the phenomenon by giving a visual, sound, scent and/or electhcomagnetic indication. Further a method for detecting exposure to a physical or chemical phenomenon and indicating the exposure is presented.