## 4 Discussion
Although the mobility intensity and scene durations were not described, results were fairly comparable to our data, indicating that other motion detectors can also accurately identify motionlessness [8]. Although the information on mobility constraints and exercise capacity of patients at the ICU has prognostic value, measuring their exact activity levels may not be essential during their stay at the ICU, and could also be performed later during rehabilitation. Most importantly, motion detectors are not regularly used for this indication at the ICU. As motions are a relevant source for the inaccurate reading of vital signs, motion detectors were further tested to reduce the number of false alarms for the conventional monitoring system [12]. In recent years, newer noncontact techniques have been developed and practices introduced to replace the traditional contact-based monitoring systems that concentrate on estimating heart and respiratory rate via, for instance, video-based photoplethysmography or mid-wave infrared (MWIR) thermography [28; 29; 30]. The detection of motions in this area was performed primarily to reduce or blank out motion artefacts [30]. These techniques were primarily tested and applied in pediatric cohorts, as the significance of contactless monitoring is more meaningful here [31; 32; 33]. Noncontact monitoring using imaging techniques was also introduced in adult patients with dementia, but the procedure was still susceptible to errors, and safety was not regarded high enough to justify substituting the current standard in clinical practice [34; 35]. Imaging techniques have another major disadvantage: continuous video surveillance or video recording with commonly accessible visualization of highly private patient ambience is difficult to justify from an ethical and privacy rights perspective, especially in delivious patients. There are legal concerns from the medical staff regarding video recordings at the ICU, as videotapes could be used to monitor and evaluate the daily work of the co-recorded employees [36]. Although privacy-observing imaging techniques such as thermal imaging or 3D depth cameras are primarily used to detect body movements [22; 23], the difference to a real camera might not be detectable for the monitored subject. Thus,noncontact monitoring systems without privacy breaching potential should be the preferred modality in the ICU. Radar measurements to detect patient motions might be an alternative method compliant with data protection regulations [23]. However, the roll-out of stationary radars in an ICU room would imply larger-scale construction modifications, which may limit their use for cost and feasibility reasons. Any new device comes with the risk of inducing false alarms [37]. According to our concept, motion detector alarms should only be triggered if the traditional system is detached and motionlessness is detected. If motions do not trigger the alarm, the number of false alarms should be low in agitated patients who constantly move around. Accordingly, the number of false negative test results (\"motions not detected but recorded\") in our study was very low (3.9%), signifying high sensitivity for detecting motions. Clinically, a false negative test result (as observed in patients falling asleep) indicates that a \"false\" alarm was activated without an actual emergency. Thus, the walk to check the patient's condition would have been unnecessary, which again may provoke alarm fatigue with all its consequences [6]. A suitable way to reduce false negative results triggered by motion detectors could be achieved with another promising sensor type. Noncontact intrinsic optical fiber sensors can be easily installed underneath a patient's pillow, enabling monitoring of heart rate and breathing frequency [24; 25]. They also have a motion-detecting function, primarily used to recognize disruptive effects and blank out \"false alarms\" [28].