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Comment by tzs | Hacker News Reader

I'm concerned about this feature, described on their home page:

> If you use an iPhone 4S or iPhone 5, you can enable Lockitron to sense when you walk up to the door and unlock for you using Bluetooth 4.0. We call it Sense.

Can it sense which side of the door you are on? If I'm coming in from outside, then having the door unlock as I approach would be useful. If I'm going to the door from inside, to look through the peephole to see who is pounding on the door and yelling for me to open it, I would not find it helpful for the door to unlock itself.

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We're experimenting with this feature and really want it to work. We will keep refining it going forward. One really needs two radios or some very clever math to determine which side of the door one is on.

What we have done for our development version is set it up so it can be in one of three modes. Always on (for passageways) so it consistently locks as you walk up and unlocks as you walk away. Always off (always disabled). Or Manual override.

With the Manual override it still unlocks as you approach and locks again as you depart, but it also allows you to lock the door by hand after you come in and will stay locked until you manually unlock it by hand again or send it a direct command from your phone. This way it doesn't unlock randomly while you're walking up to the door to answer it.

It's our first pass at making this particular feature happen.

"Always on (for passageways) so it consistently locks as you walk up and unlocks as you walk away."

I don't want my door toying with me like this.

At least it doesn't feature Real People Personalities, although I am pretty sure Sirius Cybernetics has a patent on that. ;)

We've toyed with the idea...

If you know where I am every few minutes, you can tell whether I am likely to be coming or going.

I started to write my own version of this a while back but, it relied on some "server-side" work.

I had a daemon running inside my house which looked for my iPhone on the internal WiFi network. When my phone went off-line it signaled that I had "left" and after a certain duration went into "watch-to-unlock" mode. When my phone reappeared on my network I would signal to unlock.

I know you are probably trying to keep as much of the logic off the perimeter of your ecosystem (Phone App and in-home hardware) but, it was the best way I could figure it out.

So the whole time you were home, your door was unlocked? Even while you were sleeping?

Maybe he lives in Canada. :)

You should be able to figure out if the signal is coming from inside vs. outside based on signal attenuation. Systems are being developed to pinpoint user location indoors based on this technique. Fortunately, your use case is more binary: Is the bluetooth signal passing through a door. Any dBm above a certain number would just be assumed indoors.

Great stuff and good luck!

Have you considered a patch antenna or something similarly directional right on the PCB? Still only one radio and reasonably robust direction detection as far as "is the signal coming from in front of me or behind me" is concerned.

This could be an added incentive for customers to purchase your hardware for both their front and back doors. Then they've got two radios.

In two-door installations, it may be possible to look at the signal strength as received at the back door to tell when the user is inside the house. That could get you out of the time-of-arrival calculation business.

Another possibility is a small, cheap IR sensor. If there's a person inside the house within ~10 feet of the door, it doesn't unlock automatically. The basic idea would be similar to the sensors on toilets and urinals in public restrooms.

In any case I'm glad to hear that my Tom Swift amulet is finally being made. Next up, the Triphibian Atomicar!

Nice, if you put an IR sensor on both sides then you can easily bias it (and not do anything if both are active - manual unlock is fine in that case)

Sunlight will be an issue though...maybe IR and ultrasonic?

For what it's worth, I have some home automation setup that checks for my iPhone's presence on wifi (my phone gets on wifi every ~10 minutes on battery, and holds a connection when plugged in). I preordered a Lockitron, and plan to use the API in my "welcome home" script trigger to unlock the door.

I'm not sure how easily you could implement this sort of detection on Lockitron's end, though. I use a static DHCP lease on my router and simply ping the phone.

Just thinking out loud here! Wifi presence seems super useful from my limited experience, and I'm not sure why more tech things aren't using it.

What we have done for our development version is set it up so it can be in one of three modes. Always on (for passageways) so it consistently locks as you walk up and unlocks as you walk away.

Don't you mean the other way?

You already have another radio: the Geolocation stack in the phone itself. It can't tell you precisely what side of the door you are on /now/ but it can certainly be used to infer how long you've been near the house and thus, where you're likely to be.

So say if I've been GPS "home" for five minutes it assumes 'inside'. Then when a Bluetooth sense happens next it is extremely likely I'm going outside. Do not unlock.

Same three minutes without a BT sense pass, it's now nearly certain I'm "outside" still instead of going in and out. Coarse GPS event happens showing the phone is moving from the home geofence? DEFINITELY gone. Do unlock when the next BT sense happens.

Edit: I don't think I'm being clear enough on this telephone keyboard. I feel that with enough GPS logic and location history you should be able to infer when the user is likely home and thus disable auto-unlock. This all explodes when two locks are used, though... Or two authorized users... Or two egress points... Hrm. This is hard. :)

We gave something like this a shot (and missed). Collecting background GPS data and transmitting it to a third party service in the background is currently hard and battery intensive. Highlight does it though!

There are some good ideas in here. Thank you.

It seems like this could be a good use case for geofences.

I wish you the best of luck! Your product is one of those things that everyone will have sooner or later.

Then (as is the answer to many of the security concerns people have with Lockitron) just don't enable that feature.

Also, anyone that's seriously worried about the security of this device should be mostly concerned that the standard keyhole still exists on the other side of the door because they're trivial to bump or pick.

To play devil's advocate, it is less conspicuous to open a door that you can hack open with your phone than it is to pick or bump it (Although depending on your skill, picking it may be a very easy thing too).

Lockitron will send you a message when the door is unlocked, even if it's using a bump key.

I wonder what the minimum viable wifi-jammer is here?

Have you considered any sort of pingdom style monitoring for that sort of thing?

(Obviously, it's a really unlikely scenario right now, but if they can keep it off the air long enough to open the door and introduce it to Mr Big Hammer, notifications may not be forthcoming :) )

The minimum viable radio jammer is a high voltage spark. Not very subtle or safe though.

http://en.wikipedia.org/wiki/Spark-gap_transmitter

Building a proper one is still pretty easy. It's carting around a big enough battery that's the problem.

It probably has a proximity timeout -- if you're out of range for more than x number of minutes, it will consider you 'gone'. It may not be passive, and may send you a request via Bluetooth for unlock. I imagine they have this worked out well enough to advertise it :)

Maybe a cool feature would be if it didn't unlock automatically, but put it in "unlockable" mode, and would unlock when you knocked on it. You would still have the convenience of unlocking automatically (if your hands are full, use your knee or something), and it wouldn't unlock when you're in the house

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