Using fermionic techniques, we compute exactly the large deviation function(ldf) of the time-integrated injected power in several one-dimensionaldissipative systems of classical spins. The dynamics are T=0 Glauber dynamicssupplemented by an injection mechanism, which is taken as a Poissonian flippingof one particular spin. We discuss the physical content of the results,specifically the influence of the rate of the Poisson process on the propertiesof the ldf.