Quick reply from Cateye:
Thank you for your interest in CatEye products!
The Stealth 50 should be fine for your tandem application.
Without optional accessories, the Stealth 50 gets it's speed signal from the GPS satellite, so there is no limit to the GPS-based speed signal "range" per se.
The optional "ISC-11" ANT+ speed/cadence sensor has a 5 meter wireless transmission range, which again should be more than enough for a tandem application. Note: If the Garmin speed/cadence sensor is ANT+, it can also be synched to the Stealth 50 computer head unit.
See Stealth 50 product details at
http://cateye.com/en/products/detail/CC-GL50/.
See optional ISC-11 sensor details at
https://www.shopcateye.com/product/a...-sensor-ics-11.
Find an authorized CatEye dealer near you at
http://www.cateye.com/en/shop/.
CatEye Customer Service
Sounds good. The Garmin 800 reads the Garmin chainstay sensor signal from at least 15' away, so it's a problem with the Node, not the sensor.