Inclusion Criteria:  Informed Consent as documented by signature Age 18 years or older Sex: male Diagnosed with underactive bladder (UAB) (confirmed with urodynamic testing)  Exclusion Criteria:  Acute urinary tract infection Patients on anti-coagulants (exception Aspirin) Penile pain (NPRS score >2) Pain during voiding (NPRS >2) Penile lesions (NRS score >2) Hematuria >2+ Mechanical subvesical obstruction (confirmed by cystoscopy) (exception BPO) Transurethral resection of the prostate (TURP) less than three months before visit 2 Penile abnormalities (Buried penis, Peyronie's disease, skin lesions) Asensitive bladder (no sensation of bladder fullness) Shy bladder Indwelling transurethral catheter Inability to understand and follow the study protocol Previous enrolment into the current study Enrolment of the investigator, his/her family members, employees and other dependent persons Participation in another interventional clinical trial within 3 months prior to visit 2 or planned participation during the trial Lacking capacity for consent