Deck Locks are a sensible way to hold high running rigging loads with a relatively inexpensive device that keeps a set adjustment and which will release automatically when overhoisted.
The system requires a short length of wire to be spliced into the line and a swage is placed on the wire. This swage is loaded into the deck lock easily and is then released so that the tail can be removed. It is considerably cheaper than a winch or a jammer.
Notable yachts to carry deck locks have started with Fisher & Paykel (Whitbread Maxi Ketch) for both main and mizzen halyards circa 1988. Since then a number of yachts have carried them, The wallygator 105 is another prominent example. Pricing for these starts at NZ$100. They are machined out of solid alloy, but the relatively small light nature of them and their simplicity make them a very inexpensive item especially when compared to jammers which will wear out the rope if always held in the same place.