Smarty House Part 8 – Locks But No Bagels


Note from the editorEditor’s Note – This is the eighth part of an ongoing series by journalist and geek Marty Winston in his quest to design the perfect smart home of the future with the best technology of today.

What’s the easiest way to get into a house, uninvited? Easy: through an unlocked door. Know what the second easiest way happens to be? A locked door. This is about tech, so we’ll put more attention there than on the why’s and wherefore’s of needing it.

Locking and Unlocking the Door

Locking and Unlocking the DoorIt’s amazing how many intruders enter a home through an unlocked door. Even when the front door is locked, there may be easy entry through a garage door, side door, or back door. Nobody’s perfect; any of us may be a little absent-minded. Here is something that automation can address; and in a moment, we will, but first…

Let’s not give a back seat to unlocking the door.

If there’s a fire, it’s important for people to get out without needing keys or codes or hardware to make a safe escape; ideally, an inside knob should always turn freely to allow immediate egress. You might also want to let automation unlock all the doors during an emergency to allow first responders easier access. For an electric lock, the buzz terms are fail-secure or fail-safe for the way they behave during power failures. A fail-secure door stays locked while a fail-safe door is unlocked; our choice is fail-safe.

You might want automation to make sure all of your doors are locked at bedtime, or when there’s a strong potential for trouble outside the walls of your house, and to make sure they’re all unlocked when there’s a strong potential for trouble inside, especially if there’s some subtle way to notify first responders.

A Key Consideration

You can make up your own mind about this, but our thoroughly considered opinion is that a traditional metal key should always be able to lock and unlock any door. A key works when things that use batteries may not or when Wi-Fi or Bluetooth gizmos may not be handy.

A key considerationWe just asked a lock manufacturer about the best kind of key lock cylinder to foil most attempts at forced entry. Short of a high-security installation, the answer is a 6-pin cylinder, a little more secure than popular 5-pin lock cylinders.

We’ve explored alternatives to keys. Button pads tend to show the additional usage wear on those buttons that are part of the unlock code; that reduces a 3-digit code to needing no more than 9 trials to get it right, or 16 for a 4-digit code. That’s not terribly secure.

Fingerprint readers are not reliable enough to always recognize you on a first (maybe second) try. Radio links, whether Bluetooth or Wi-Fi (or Z-Wave or Zigbee), depend on you having a device that can transmit a code, that’s unlikely to get broken and that won’t lock you out every few months when batteries die.

All of these approaches are vulnerable to dead batteries. Keys aren’t.

Let’s Twist Again

OK, so a key turns to lock or unlock a door and we know that works. Every electronic door lock home automation product we’ve ever seen has used one of the above approaches in conjunction with something big and not especially attractive to hold batteries.

To be accurate, they’re electronic deadbolts. If your standard doorknob has a separate lock, opening an electronic deadbolt may still not let you in.

That’s enough complaining about the products that we don’t like. Let’s take a look at an approach we do like. It’s more expensive, so it will be a considered purchase.

Meet the Deadlatch

springlatch door latch
springlatch door latch

The latch on your closet has a half-round face to help push it out of the way as you close the door, then a spring inside pushes it into the hole in the door frame, inside the striker plate, that lets its flat side keep the door from just pulling open again. That’s a springlatch. You may have had occasion to open a locked spring-latch door with a piece of wire or plastic by moving it along the curved face, getting it out of the way again. You can lock a springlatch doorknob but it’s not a very effective lock.

A deadbolt is a square-faced round or oval rod that you get to move in or out of place by directly controlling it. There’s no curved face to finesse.

deadlatch door latch
deadlatch door latch

A deadlatch looks a lot like a springlatch except for an added bar along the flat side. That bar can keep the door locked even if you manage to push the round-face part out of the way.

We should also mention Kikgard, a piece of metal that can stop a gorilla from kicking in your door. Cops who do that on the job know that the weak point in the door is the place on the door Kikgard powerful doorstopframe trim where the striker plate mounts, so a good kick there lets the door open wide. Kikgard mounts on the back of that piece of trim to tremendously stiffen it, spreading the stress of a kick across a wider path and providing a rigid back strut for the frame. It’s a little like putting a steel sleeve over a toothpick to make it a lot less easy to break.

It’s Not Newer, Just Better

electric lockOur better answer, the electric lock, has been around for generations. You have lots of choices; the one we like is the Schlage D80PDEL. It has a keyhole on the outside and a key can always operate it. It has a plain knob on the inside and simply turning that can always let you in or out.

It also has a solenoid that works on 24 Volts at a fraction of an Amp. In this fail-safe model, powering that solenoid locks the door and removing power unlocks it.

For us, that means a ten-buck power supply and a three-dollar relay to let our automation control it.

ives electric hingesWe should also mention Ives electrified hinges that let us invisibly pass power from beyond the door frame all the way to the lock. There’s nothing about the lock that looks electric; it just is.

Our automation can control the relay that controls the lock; the same automation also connects to a magnetic reed switch in the top of the door frame, which closes when a magnet in the top of the door faces it, so the automation knows when a door isn’t closed.

We probably don’t need to tell you that exterior doors are well targeted by our surveillance cameras.

The Weakness: You

No home door lock is perfect because no occupant is perfect.

When somebody comes to the door wanting to inspect this or that, or to use your phone, or to hit you up for a charity, or to ask for a handout, or to offer to do odd jobs or with any of scores of other pitches, congratulations, your home has just been selected as a likely target for thievery or, worse, burglary. (Theft does not necessarily involve forceful entry while burglary does).

Here are some rules for that: Don’t let them in. Do immediately call law enforcement and let them know all you can about who came, what they claimed, what they look like, how they’re dressed and the kind of car they had. You may not fall for their con but when police know they’re working a neighborhood you may be able to spare your neighbors some grief.

If you can snap a quick smartphone picture, so much the better. They may try to bluff you with “invasion of privacy” or some other nonsense, but they’re on your property. You can always just say you were taking a picture of your front yard and they got in the way.


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.