A wearable system to constantly monitor the bruit generated by an AV fistula at times other than during dialysis was developed, and provided early detection of rapidly developing thrombi that cause occlusion of the fistular vessels. The system consists of a downsized microphone that continuously monitors the bruit generated, a warning device worn like a wristwatch, and a wire running down from the microphone to the emergency warning device. The microphone converts the bruit into an electrical signal and outputs it to the warning device. The emergency warning is then sounded whenever the input signal from the tiny microphone is weaker than a preset level. The warning device was set off in 4 of 21 long-term dialysis patients with arteriovenous fistulas, and within several hours all 4 developed an occlusion. One of the 14 patients with a graft had the device go off while sleeping, but it was a false alarm due to positioning that resulted in compression of the fistula arm.