The ResMed warranty says, in part "...the warranty does not cover any damage caused as a result of... modification or alteration of the product."
Does replacing the SD card in an AirSense 10 AutoSet for example constitute a "modification or alteration" of the product?
Has anyone had difficulty getting their ResMed APAP machine repaired under warranty because they replaced the ResMed SD card with, say, a wifi SD card?
In 4 years on Apnea Board, I haven't heard of anyone running into warranty problems because they swapped out the SD card. It's a consumable item, just like the filter or the humidifier chamber. If you want to be safe, you can put the original away in a safe place, and put it back if you need to send your machine back for warranty service. There is no way to detect if you've changed SD cards other than by looking at the label.