According to an aspect, there is provided a handheld device (2) for applying energy pulses to skin (17) of a subject to perform a treatment operation as the handheld device is moved across the skin, the handheld device comprising: an aperture (6) that is to be placed adjacent to the skin； at least one energy source (8) for generating an energy pulse and for providing the energy pulse through the aperture to perform the treatment operation on 5 skin adjacent the aperture, wherein the at least one energy source has a minimum pulse repetition period following the generation of an energy pulse before a subsequent energy pulse can be generated； a first skin property sensor (14) for measuring a skin property and for outputting a first measurement signal representing measurements of the skin property at a first sensing position (24), wherein the skin property is a property that changes in response to the application of an energy pulse to the skin, and wherein the first sensing position is in front of the aperture relative to an intended motion direction of the handheld device over the skin； a second skin property sensor (16) for measuring the skin property and for outputting a second measurement signal representing measurements of the skin property at a second sensing position (26), wherein the second sensing position is behind the aperture relative to the intended motion direction； a memory unit (56)； and a control unit (10) that is coupled to the at least one energy source to control the generation of energy pulses by the at least one energy source, and coupled to the first skin property sensor and the second skin property sensor to obtain the first measurement signal and the second measurement signal, wherein the control unit is configured to store a profile of at least the first measurement signal in the memory unit； wherein the control unit is further configured to, when the handheld device is moving in the intended motion direction over the skin: analyse the profile
