Power consumption is a critical factor that determines the lifetime of a wireless network node. Substantial portion of the power is consumed by the transceiver in the transmit phase. This paper presents a new SNR detection technique for dynamic power management of ad-hoc wireless network nodes. The technique is based on the spectral analysis together with a predetermined spectral mask of the received signal. The peak power of the transmitting party can be adjusted according to the SNR information computed at the receiving end. In this way, each wireless network node transmits at the minimum power level avoiding dropped packages. Measurements on sensor network nodes, we have determined 50% potential savings in the average power consumption of the overall node. Experiments on a small network show that the power management scheme provides 65% power savings.