  Current parameter estimation techniques rely on photodetectors which have low
brightness and thus are based on gathering averaged statistics. Recently it was
claimed that perfect photodetction will change the nature of sensing algorithms
and will increase sensing efficiency beyond the immediate effect of having
larger collection efficiency. In this paper we bring up the observation that
perfect photodetection implies Heisenberg scaling($\frac{1}{T}$) for parameter
estimations. We analyze a specific example in detail.
