Developers at ActiveCaptain have developed an anchor alarm for apple and android products. So, most of you out there can use your smartphone as an anchor alarm to notify you when your anchor is dragging.
The app allows you to enter the lat/long of the anchor and length of anchor line deployed. You specify a “acceptable” drag distance, alarm delay and wah lah! Your smartphone becomes an anchor alarm. It determines if your anchor is dragging using GPS and notifies you.
The app is available on iTunes for free here: DragQueen