In the context of battery powered radios people usually think of things like remote sensors that spend most of their time sleeping and only need to be woken up when data needs to be transmitted. This scheme can allow for weeks or months of battery life.
I'm thinking of a similar thing, except that it is a battery powered radio that briefly wakes up to listen for a transmission from a base station. Are some radios more power friendly at doing the sleep-listen-sleep cycle than others? Or to put it another way, which radios have the smallest power penalty for simply energizing their receive circuitry for a few milliseconds?