Good question (i’m not here to sell anything btw). Just sharing my 5 years of work 
This is where the sensor is being placed, at chest height under the matress sleeve.
It’s a ribbon of about 90 cm long, logging each minute a resitive value.
If You want to heave a look in our science base, please have a look at www.q-strip.com
Hope this information was useful.
Cheers!
Daan