Frontline Defense Full-Size Latch Guard

Sept. 19, 2022
Preventing attacks and bypasses on aluminum storefront doors can be achieved in less than one hour.

Aluminum storefront doors handle all sorts of abuse, and that’s just from regular use. They also have to stand up to attack from criminals, including those who use a prybar, a saw or even a special tool aimed at locksmiths that allows them to defeat an Adams Rite hook bolt deadlock.

However, locksmiths have a new tool in their arsenal that can stop all of those attacks — an interlocking full-length latch guard. The piece of door hardware is made by Frontline Defense Systems in Edmonton, Canada, and the installation of it was the subject of a recent meeting of Locksmiths United.

The Interlocker

The Frontline Defense Interlocking Astragal, or Interlocker, is two pieces of aluminum (or steel for hollow metal or wood doors). One piece is installed on the door, the other on the frame. The full-length U-shape notch on the door piece interlocks with the L-shape piece on the frame to eliminate the gap in the door and prevent access to the lock bolt and, thus, a prybar or other types of attacks.

Ron Murray, who owns a locksmithing company in addition to Frontline Defense, said he saw early on how successful the product was after a run of break-ins on one side of a street. He installed the product on nine doors on a set of buildings and the break-ins moved across the street.

“A month and half later, the guys on the other side of the street said they needed 14 of them on their complex,” Murray said.

A more recent convert was Wayne Winton of Tri-Country Locksmith Services, located in Glenwood Springs, Colorado. During the meeting, Winton demonstrated an installation of the Interlocker on an aluminum storefront door.

“This is a no-brainer and an easy moneymaker,” he said of the Interlocker, adding that the entire installation takes less than an hour.

Winton said all he has to do to make the sale is show a video of the easy defeat of a storefront door that has a hook bolt lock to the owner, “and they’re in a hurry to hand you a fistful of money.”

The Installation

The tools necessary for the installation of a storefront Interlocker are as follows:

  • Drill
  • 3/16-inch metal drill bit
  • 9/32-inch metal drill bit
  • Step bit
  • Heavy-duty rivet tool
  • 3/16-inch Allen wrench
  • Hammer
  • Combination square
  • Level

Another important tool comes with the Interlocker, as Winton and Murray pointed out — the packing foam, which is used to help to align the two interlocking pieces.

Because the Interlocker is a full-size latch guard, any door hardware that would overlap with the Interlocker has to be removed from the door at the outset. In Winton’s installation, that meant removing the cylinder, door handle and latch.

Murray noted that any strike lip that isn’t flush with the frame has to be cut down so the strike won’t impede the interlocking nature of the latch guard. The same is true of any bolts or blind nuts that might prevent the Interlocker from being flush to the door and frame.

“All of [the reinstalled hardware] will help to hold the latch guard in place,” Winton noted. That also means that the holes for the cylinder and handle have to be redrilled through the latch guard. For the handle, Winton advised drilling the hole all the way through the door to use as a template for the latch guard.

The L-shape latch guard piece then is attached to the frame by using the 3/16-inch drill bit to drill through the Interlocker roughly 1 inch from the top and then into the frame. Frontline recommends then doing the bottom the same before marking even lengths of 14–18 inches between the two points. Rivets then are popped into place, and you should make sure that the gap in the door remains consistent and the L-shape piece is plumb.

Winton noted that having sharp drill bits is important to save time and wear on the body and added that he includes the price of new drill bits in his install quote.

Foam Comes Into Play

The packing foam comes into play when installing the U-shape latch-guard piece on the door. The foam that’s used to keep the latch guard pieces separate in the box is again used to separate and align the two pieces during the installation so there’s no binding later on.

“I like to follow the natural door lines, just again to keep everything aesthetically pleasing,” Winton said.

The U-shape piece is attached by through bolts that require the 9/32-inch drill bit. Winton advised starting with the 3/16-inch bit to save wear on the drill bit before moving to the larger bit. The bolts should be even with the rivets on the L-shape piece for a clean presentation.

“I like to drill all the holes first and then add the bolts,” Winton explained. “Picking up one tool and putting it down for another constantly takes up my time.”

Another piece of advice: If there’s vertical linkage in the door, you can’t use through bolts, only rivets to attach both pieces. This also is true for a double-door installation, and Frontline Defense has Interlockers to handle that application.

With the latch guard in place, the final step is reattaching all the door hardware. Winton used the hole for the interior cylinder as a template for the exterior cylinder and then reattached the hardware in the reverse order that he took it off the door: handle, hook latch, cylinder.

One final note: If you use a cylinder collar, you might have to remove a ring from the cylinder because of the added depth of the latch guard.

Winton noted that although the latch guard now effectively has prevented bypassing or a brute-force attack against the latch, the other side of the door’s exterior might be vulnerable. That’s where a continuous hinge comes in, which Winton’s door already had.

Between the Frontline Defense full-size latch guard and the addition of a continuous hinge, “how much bigger and beefier does that make the door look, Winton said. Just the intimidating look makes criminals go somewhere else.”

Murray said the Frontline Defense Interlocker comes in 11 different colors. For more information, go to

Go here for a video of the meeting.

Locksmiths United

Locksmiths United is a monthly Zoom presentation to discuss locksmithing and provide information to others in the industry. The meeting is scheduled for 7 p.m. ET, the first Monday of each month. All locksmiths are invited. Contact Winton via Locksmith Nation’s group page on Facebook for the Zoom link.