Source: The Coolest Gizmos and Gadgets; February 2010 ACBL BRIDGE BULLETIN
Most players do not have a cool gizmo or gadget to use over auctions by the opponents, such as 1NT-3NT, 2NT-3NT or 1NT-2NT-3NT. You will pass almost every time, and partner will make his normal lead. But how would you like to double 3NT to ask partner to lead a heart? I love it! The gadget is called the Elwell Double (its inventor was J.B. Elwell). Why hearts? Why not? The way I learned this treatment is that this double calls for a heart lead. I’m sure that in other parts of the country players have a similar bid that calls for a spade lead or a minor-suit lead. Their gadget will be called something else. That’s okay.
Two important things to remember: The Elwell Double (Alertable) never applies when the opponents have bid a suit, either naturally or artificially. Therefore, only notrump bids have been made. Second, your partnership hasn’t bid either.
Say I am in fourth seat and pick up: 
74 
AKQJ10 
543 
765 and hear left-hand opponent open 1NT and RHO jump to 3NT. This is an Elwell Doubler’s dream hand. I double and call for a heart lead and they go down like a shot. How often does this happen? Not very. But I will wait.
Say LHO opens 2NT and RHO raises to 3NT and I hold: AKQ103 A 8754 432
I am going to double and take my chances that a heart lead will scuttle 3NT. Maybe partner was going to lead a major anyway. Fine. Maybe they only have eight tricks no matter what partner leads. Fine. But this way they go down doubled! What if one opponent has the J-x-x-x of spades? That’s life in the big city.
Think of the psychological warfare that goes on here. Doubling freely bid contracts raises the adrenaline level of everyone. Partner may wake up from a short nap and usually the result will be that partner will defend as well as possible. The dummy will be sweating bullets and may panic and run. The declarer may get a case of the jitters, because to tell you the truth, every time I use the Elwell Double, I do not have the perfecto example hand of the AKQJ10. Sometimes I decide to use it when I have something like the AKJ10xx. Be sporting about it. With that heart holding, one thing you know is that either the opener or responder will have nothing in hearts and may not know what to do. Put them to the test. Sometimes the player with nothing in hearts will run when it turns out that partner held the protected Q-x-x. By doubling freely bid notrump game contracts in this way, it will test even the most seasoned partnerships, while you have a huge chance of a swing in your favor.
Some sophisticates play that if the opponents double a notrump game out of the blue like this, a redouble by either one of the bidders shows doubt, while a pass would imply a stopper. In fact, I like to play it this way. Everyone is then rolling the dice and is forced to use judgment.
The opponents may win a hollow victory. They might run to four of a minor and make it when 3NT was going down doubled, but no other pair in the field had the Elwell Double to use, so everyone else was bidding and making 3NT on the normal lead. The opponents were plus 130 instead of minus 200, but it was the same zero. Oh, well.
I have also seen pairs run from 3NT doubled when it was cold, and I have had many pairs sit it out only to get crushed. The one thing that has always been true is that when the Elwell Double strikes, it is always fun, and it usually leads to a terrific result.
The pleasure that arises from a great gizmo or gadget coming up enhances the whole session. Even if it fails, the opponents may develop a future fear of you, and that type of fear can last a bridge lifetime. Once a pair is scared in some way, it sticks in their subconscious and can pay dividends over and over. You know what I am talking about. People will remember that you are not a run-of-the-mill partnership and that even the simplest of auctions can put them in jeopardy.
Add the Elwell Double to your bridge arsenal and you will have one more great gadget to look forward to using just when it is least expected. If you add a dozen cool gizmos and gadgets to your partnership, the odds go way up of one or more of them coming up from time to time. I’m ready to go play just thinking about this!