Accidental venous needle dislodgement during hemodialysis may cause serious bleeding including a sometimes fatal outcome. The venous pressure gauge of the dialysis monitor does not react when dislodgement occurs. A sensor patch put as an adhesive over the venous needle puncture site connected to an alarm unit by an optic fiber has been clinically tested in 5 dialysis departments. A small amount of blood on the sensor activates a light and sound alarm. A simple questionnaire was filled out by the nurses at each dialysis concerning their feeling of safety when the new device was used. Forty-one patients, mean age 65 years, have tested the new safety device. Two hundred test dialyses were studied, after exclusion of 13 tests. One hundred seventy-nine tests reacted positively on blood. In another 6 dialyses, a warning light appeared on the alarm unit indicating a failure in the sensor patch. Thus, the alarm functioned in 92.5% of all tests. After a small modification of the sensor patches there were only 2 dialyses (2/71) without an activated alarm on blood, i.e., 97.2% positive alarm reactions. The answers of the nurses indicated that they had an increased feeling of safety when using the new safety device, with a mean value of 3.4 points on a visual scale from 0 to 5 where 5 meant very much increased safety. In a situation when the dialysis monitors today do not react on bleedings from venous needle dislodgements, the new alarm safety device fulfils a known shortage in routine dialysis safety. In situations where supervision during a dialysis session may be insufficient as, for example, in home hemodialysis and self-care dialysis or in other situations when the patient is sleeping, the device may be life saving.