I will briefly review the approach of simplified models for dark matter phenomenology. I will then discuss non-standard strategies in dark matter model building, characterized by a feeble coupling between the dark matter and the SM particles, which lead to novel and exotic signatures at the LHC in terms of longlived particles. In particular I will focus on the Singlet-Doublet dark matter model in the regime where the dark matter abundance is obtained via the freeze-in mechanism. As a consequence of the small couplings, the heavier particles in the model are long-lived with decay length at typical scales of collider experiments. I will analyse the collider signatures of the model, characterised by displaced h/Z bosons plus missing momentum, employing current LHC searches for displaced vertices and missing energy to significantly constrain the model. I will also take into account the cosmological bounds relevant for the light dark matter candidate. The outcome of this analysis emphasises the generic interplay between displaced signatures at the LHC and cosmology for dark matter candidates whose relic abundance is obtained through the freeze-in mechanism.