is being filtered by both the bedframe and mattress. The other common sensor placement is between the bedframe and mattress, as in [18]. Fig. 2 presents these common PS placement locations with respect to the bed. When placing the PSM under the mattress, the mattress filtering effects must be considered. Holtzman et al. investigated the effect of nine mattress types on a PSM's ability to measure breathing rate [60]. Overall, the mattress acts as Fig. 4. (a) Hospital bed frame that must be considered when selecting PS. (b)The fiber-optic PSM (S4 Sensors Inc., previously Tactex Controls Inc. [56]) placed strategically to deal with bedframe adjustments. Table 2 - Commercially available PSM Pressure Sensitive Mat Sensing Method Description Tekscan [61] Piezoresistive Has been used in internal fluid monitoring applications XSensor [62] Capacitive ink Has been used to monitor breathing and movement in neonates S4 Sensors (S4 Sensors Inc.) Fiber-optic Has been used in sleep monitoring, immobility and mobility applications Withings Sleep Tracking Mat [13] Single sensor pneumatic (air pressure) mat Small mat that is air filled, when force is applied to the air chamber pressure is detected Emfit QS [29] Proprietary capacitive sensor Single sensor that uses ballistocardiography based on proprietary plastic technology that acts a pressure sensitive capacitor Teleheath Bed Sensor (BestBuy Assured Living) [63] Capacitive Adaptive bed sensor that uses capacitive sensing methods with some post processing causing it to act as a switch indicating if there is someone in or out of bed Eightsleep [30] Piezofilm based sensing Sensors integrated into the mattress to measure sleep quality and adjust temperature Eight Sleep Mattress Cover [30] Piezofilm based sensing Cover material placed over an existing mattress In-Bed Presence Detector [31] Sensing method is unclear Acts as a flat switch to identify if pressure is applied or not (i.e., someone is in or out of bed) Sleep Number Mattress [64] Air pressure based Integrated into a mattress Rest Smart Mattress [65] Force sensitive resistor Integrated into a mattress Beauty Rest Mattress Base [66] Passive piezoelectric sensors Two sensors located in a base unit placed under a mattress 20 IEEE Instrumentation & Measurement Magazine April 2021