A deployable device comprising a deployable member. The deployable member comprises an optical fibre. The deployable member is stowed at the device in a first wound configuration and arranged to be deployed from the device to a second unwound configuration within a well. In examples, the deployable device is configured such that, when unwound, the deployable member has a propensity to adhere to a wall within the well. In examples, the deployable member comprises at least a first length and second length, the first and second lengths having different mechanical properties.