An example embodiment of the invention provides a system and method for detecting a liquid leak that includes a sensor with a passive resonant circuit having a resonant frequency, an interrogation unit to transmit a radio frequency (RF) wave corresponding to the resonant circuit's resonant frequency, and a receiver to measure the resonant circuit's response. A determination unit is configured to determine the presence of liquid based on the measured response. In the absence of liquid, the resonant circuit radiates a signal corresponding to its resonant frequency; however, in the presence of liquid, the resonant circuit's electrical characteristics change such that the resonant circuit does not resonate at its resonant frequency. The resonant circuit may include inductive and capacitive elements formed on a substrate using electrically conductive materials. Thus, the system may quickly, safely and accurately detect potentially life-threatening blood leaks that may occur during, for example, hemodialysis.