Comment by Ohtrahddis | Hacker News Reader

Comment by Ohtrahddis | Hacker News Reader

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Wifi has always been a tricky problem for small devices. However, I think there are some good tricks that people have been using involving playing around with sleep times, skipping beacon intervals, etc. - tricks that the electric imp, the Wifi board used in Lockitron, utilizes to lower the current consumption by a bit.

You're totally correct that always-on-instant-unlock feature is a fool's errand as that would mandate always-on Wifi, spelling death for battery life.

I think one feasible method is sleeping the Wifi and using an external input (like a button or a "knock" sensor) that wakes up the Wifi, tells the chip to check the server for updated lock state, and then go back to sleep. I've played around with capacitive sensing on a door handle to wake up the Wifi and check the server as soon as someone lays hands on the door. Cap sensing is also incredibly low power so it had minimal impact on battery life.

This of course introduces all kinds of problems, but if Wifi is absolutely necessary, then this is one solution.

Either that, or wake up to poll Wifi every 5, 10, 15 minutes (destroying instant lock/unlock)

Good points.

The skipping of beacon intervals is called PS-POLL and is why I said 2mA otherwise it is closer to 100mA -- which for example is what TI's CC3000 module burns since it doesn't have PS-POLL.

I agree that there are alternative ways to wake up WiFi. They said at one point in HN that they were thinking of having WiFi wake up when you knock. The problem with this is that the experience is markedly different from what they're advertising to users.

You'd pull out your phone, bring up the app, hit unlock, then knock on the door, wait for WiFi to turn on, associate with access point, get to cloud, "see" the unlock command and then unlock the door. That's easily 7-10 seconds at best.

Screw that. I'll just take out my key.

Giving WiFi long life by keeping it off is relatively easy. Making it instantly responsive, which is what anyone using the lock would expect, is impossible at the quoted battery life.

It is kind of like selling a car saying it'll get 500mpg but not telling the buyers that you only get that if you go say 10mph.

It would be pretty easy to have a phone app that notices you're arriving home and sets the lock to open. All that's left for you to do is walk up to your door and knock.

As well, their software learns your habits over time and can be awake when it expects you to arrive.

These tricks and others will improve over time. Enough to where it's more than an acceptable experience for many, if not for you.

They actually are doing the knock to wake. BLE works and is an instant lock/unlock. Sending a command via wifi will let you know (on the phone) that the lockitron is in a power save mode and the command will be executed in 20 minutes (or whatever the actual time) or when you knock on the door. So if you leave the house and forgot to lock the door, you could lock it remotely and know it'll lock itself eventually. Knocking does work consistently to wake the device up.

It's definitely not the same experience though. I live in a condo and have the lockitron on my unit's door. I have the choice between opening the lockitron app in the elevator and send the unlock signal via wifi, but that means I'll need to knock for sure. Or I could wait until the elevator gets there and try to unlock, and if i'm really lucky it will be via BLE and unlock instantly, but generally the BLE hasn't managed to connect yet and I get no indicator, so I send the command to early and I need to knock anyway.

Speed is such a critical factor here. It doesn't take that long to pull your keys out, and it feels more awkward to stand and wait at your own front door than it does to fumble with the keys for a while. If I'm carrying groceries or a baby, then Lockitron has the potential to make things easier, but currently I still need to fiddle with my phone for a while (maybe in the elevator, but still) and knock so it doesn't really feel easier than using a key.

What would your insurance company say if you said "well I knew I forgot to lock the door, but I sent the command and I know it locks itself eventually"? It's cool but not really a mass market product.

The reaction would probably be better than "I didn't know I forgot to lock the door" or "I knew I forgot to lock the door, but was too lazy to go home and so I hoped for the best."

Plus, locks are trivially pickable, so it's not like they stop someone that wants to break into your house from breaking into your house.

Locks are not trivially pickable. It only looks that way if you watch a skilled person do it. It's much harder than many impressive juggling tricks, for example. Smashing in a window, now that's trivial.

Neither matters though, because a big purpose of locks is to show that you took reasonable precautions in order for your insurance to be valid. (YMMV, IANAL, etc. but that's the case here.)

I'm about as unskilled a lockpicker as you can get, and I can pick the four-pin locks on my apartment fairly easily. Someone with practice could do it even more easily.

(I've never used a pick gun, but I hear that makes it even easier. Especially for locks that don't have any particular anti-picking features, like the majority of locks on people's homes.)

In the U.S., there usually isn't any language in a homeowners policy about doors being locked, so if you have a police report, they don't say anything.

Ah, I didn't know that. That's one less issue for them to worry about.

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