The continuous monitoring of driven-dissipative quantum optical systems provides key strategies for the implementation of quantum metrology,? with prominent examples ranging from the gravitational wave detectors to the emergent driven-dissipative many-body sensors.? Fundamental theoretical questions about the ultimate performance of? such a class of sensors remain open—for example, can they achieve quantum-enhanced precision scaling without squeezed input; how to perform the optimal measurement to approach their ultimate precision In this talk, I will present our recent efforts towards answering these questions. In the first part I will introduce dissipative criticality as a resource for nonclassical precision scaling for continuously monitored sensors, by establishing universal scaling laws of the quantum Fisher information in terms of the critical exponents of generic dissipative critical points. In the second part I will present a general quantum noise cancellation strategy to retrieve the full quantum Fisher information from the nonclassical, temporally correlated fields emitted by generic open ? ?quantum sensors, thereby to achieve their fundamental precision limit.