Knock uses a combination of an iPhone app (currently offered at an introductory price of $3.99)  and a Mac app (available for free at Knock’s website) to enable unlocking of your Mac, wirelessly, by just knocking the back of your iPhone.

It’s a surreal experience. After a couple of minutes of initial setup, you lock your Mac and rap the back of your paired iPhone twice. Your Mac unlocks. The app doesn’t even have to be forefront on your phone, although it does have to be ‘open’ in the multitasking tray. In fact, your phone doesn’t even have to be unlocked. When it senses the Mac is near, a notification appears on the lock screen instructing you to knock. There are some nice UI touches too. For instance, echoes of the ‘sound wave’ appear on OS X’s lock screen in real time as you knock. It’s a subtle visual indicator that the system is actually working.

The app uses Bluetooth Low Energy to communicate with the target Mac. This is what allows the app to operate whilst backgrounded (using the CoreBluetooth API’s originally introduced in iOS 5) and it also means that battery drain on the phone is minimised. In order to take advantage of this neat effect, naturally, you need a recent Mac and iPhone (4S or later) that has Bluetooth 4 compatibility. Helpfully, the Mac menubar utility will tell you during setup if your computer is supported.


In practice, the system failed on me a couple of times in testing. The phone just couldn’t detect my laptop’s presence. Quitting the app and reopening remedied these connection issues, however.

As a gimmicky party trick, this is the best thing I’ve seen all year. As a tech demo of Bluetooth 4 and iOS 7, it is undeniably pretty cool.

In terms of real-world utility, though, I’m not as enthused. I do not find typing a password for my Mac to be a huge chore, although to be fair I’m not in a setting that necessitates unlocking my machine numerous times a day. Regardless, as it stands, if an malicious individual manages to steal both your iPhone and your Mac, all security is foregone (as the iPhone can unlock the Mac without needing to be unlocked itself).

Knock is $3.99 for the iPhone. The accompanying Mac app can be found at the developer’s website.

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48 Responses to “Unlock your Mac by knocking on your iPhone with the new ‘Knock’ app”

  1. I wonder how many knocks it takes to crack the glass… hmm…


  2. gramsaran says:

    I’ve been using Token Lock for a while now, works the same but not limited to just an iOS device since I have an Android.


  3. PMZanetti says:

    In my personally opinion, you need to stop advertising Apps without thoroughly reviewing them. Just wasted $4 on this to have it not work at all. I’m sure its because I’m using a Bluetooth headset on my iPhone….but what am I supposed to do? Not use my headset so I can knock my Mac awake? Stupidity.

    What the hell is the point of these Bluetooth LE solutions if they are the ONLY bluetooth function your device is allowed to entertain for it to work?


  4. Well, crud. We’re sorry it failed on you even once, let alone a couple of times. If it ever fails, we haven’t done our jobs. We’ll reach out to see what’s going on here, but thanks much for writing about us.


  5. It’s funny they write that it uses “military-grade 1024-bit RSA encryption.” on their website but “2048-bit RSA encryption” in the screenshots on the AppStore.


  6. optech says:

    Totally useless!! Does not work if screen saver is active on the Mac. Need to first touch the Mac the reveal the lock screen, and *then* knock on the phone. Quicker just to type my damn password. How do I get a refund from the AppStore??


  7. Does it work anytime the Mac needs you to enter the password, like after a restart or when installing software, or does it only work when the computer sleeps and a password is needed to unlock it? If it’s just the latter, 99c would be a more reasonable price.


  8. Why would you want to knock on the glass of your $900 iPhone? You know some idiot will knock too hard and break the glass or damage something inside. Just stupid.


  9. Edmond Phon says:

    What an idiotic app.


  10. Tech says:

    That’s a weird concept. I wonder how useful it actually would be though, it doesn’t take that long to enter in a password.


  11. I think I just wasted 4$ right now. Please make better reviews on 9to5mac!
    First I noticed that the pairing did not work when I removed the knock app from the Iphone 5s multitasking tray (unlike it was promised). After re-starting the app on the phone the connection was in an undefined state. So I had to do the whole installation process from the start (which is not a big thing but does shake the confidence).
    Worst thing, since the app is running on the phone it is constantly using the GPS function. The arrow in the status line is constantly on and it’s been used by the knock app.
    Not draining the battery? With GPS on?


    • macmaniman says:

      to be fair, the arrow only suggests that an app is using the location, not the GPS per say, so if an app is using the wifi, bluetooth or Assisted-gps or the gps the arrow is still the same. so an app can in fact use your location without,,, will almost without any battery impact!


  12. Paul Nielsen says:

    I love integration between the Mac and iPhone. And super simple. Within a minute of reading the article I had it installed on iPhone and Mac and it synced and worked perfectly. #TooCool


    • Paul Nielsen says:

      after using Knock for a day, I’m unconvinced. Sometimes it works perfectly, sometimes it a knock won’t do anything, other times just touching the phone to pick it up unlocks my Mac (MBPr 15 late 2013 2.6) (iPhone 5s).


  13. Nice little trick but still buggy and unreliable. Only works once in a while for me.


  14. You have to first wake up your Mac!!

    You have to manually touch a key to wake your Mac up before knocking on the iPhone. It simply doesn’t wake on its own due to your proximity, like they make it seem in the video. When he comes over from behind the pillar they screen jump to the mac being on so you don’t see him having to wake it up.

    My experience with iPhone 5s and rMBP:

    When you walk up to the computer you have to press a key to wake it up, then a green light circles your icon similarly to the light around the Siri microphone. This is when it then begins to contact your iPhone; once the light goes solid green then can you knock on your iPhone… This can take up to 6 seconds… not a long time but since I have to touch my computer anyways I then just have to sit there and not try and type in a password.

    The knock pattern has to be have a fairly specific knock-knock pattern, too slow or too fast will result in a decline.

    The Mac app simply enters your password into the field to unlock for those of you wondering about that.

    I wish it wasn’t $4, good idea but make it wake up the Mac so whenever I reach it to sit down it is already for a knock or I can knock as I approach. I bought the Keycard proximity unlock app that does a similar thing. It appears they are all a bit lagging in speed and make themselves more inconvenient than anything else.

    I read the reviews before I bought and no one clarified this wake issue so I hope I helped someone..


  15. Relying on your review I bought it.
    However it doesn’t work very well. As you mentioned I had to quit the app on the computer several times to make it work even though it didn’t, most of the time. I’ve read the instructions, for no avail, is on and off, most of the time it says bluetooth is off when it isn’t. Waste of money.


  16. Folks! If you use a *complex* password -like you should- and if you tap the *back* of your iPhone (just hammer it) then this is blazingly fast compared to entering the password. Don’t know, what you are complaining about.


  17. I really like the app, but as Austin stated, it can take up to 6 seconds before my Mac verifies with my iPhone. The installation went great, no troubles on that. I would just like to see the 6 second delay removed in any way.


  18. s92543 says:

    I bought it after reading about it on Cult of Mac, it didn’t work first time round but after I did a restart it has worked consistently well. Though it looks like I may be the exception to the case.


  19. g04uld says:

    No thanks! The lax security in this is a real turn off for me.


  20. I have a 2012 Mac Mini and it comes up as not compatible when I try to pair with my iPhone 5


  21. don’t buy you can’t read the reviews


  22. That is the most pointless thing ever but it’s awesome


  23. mhatrey says:

    The app is great … but just not ready for its prime time,

    I do have a half hearted feeling about my purchase. Things that would make this a better app is

    1. Fix for screensaver. Common, it is stupid to wake up mac from screen saver and then knock the phone
    2. Pairing issues. Had run into this twice. I had to follow the FAQ mentioned on their website to get it fixed.

    I tried for a refund from app store, but apple says to inform the developer. Well I guess I will have to suck up and deal with $4 loss.

    The app does make a great deal for $0.99, but I guess that is just me.


  24. does not work: after having entered the password on the Mac, the Knock Mac app hangs and never finishes the setup


  25. Matt Elitt says:

    Downloaded mac app. It told me to download the knock app on my iphone. Paid 4.00. Doesn’t work probably because I have a 2011 MBP. The mac app was supposed to tell me if it wasn’t compatible and it didn’t…


  26. in a couple of words, terrible idea.


  27. Just installed the app and it’s working perfectly. However, you must accept the first question, to share data with bluetooth devices nearby. I didn’t at first installation never completed.

    The great thing about the app is, I don’t even need to knock. I just shake my phone and my MacBook Pro opens. It’s fab!!


  28. I find this app most useful when you have to unlock your Mac and people are standing so close that you fear that they’ll end up discovering your password.


  29. Ben says:

    the best part of this app is, by far, the editing and song in this video.


  30. Angelo Zodda says:

    I have a 2012 Mac book pro, downloaded the app & the mac software, i’m having problems making it work, looks like is not detecting the iPhone. or vise versa… :(


  31. Ken Ng says:

    Just thought I’d shout out. If you are on a non BT4.0 enabled Mac, just use a BT4.0 enabled dongle. If you’re running Mountain Lion or Mavericks, it should just work. If you’re on Lion or below, then I’ve a guide here( to get it running.

    Works really great on my BT 4.0 dongle on my 2010 13″ MBP.


  32. zoninyc says:


    For a ‘party-gag?’

    I’d rather spend my money on something USEFUL – let the people who seem to have ‘no problem’ being ‘first’ to buy the ‘latest, greatest’ (rhetorical question; who ‘needs’ – REALLY needs – a NEW phone every 6mos-year?).


  33. This works for me only if I wake up my 2013 iMac, unlock my iPhone 5s, open the app (even if it is already open in the background), wait around 6 second to connect to the Mac, then knock twice (not too fast, not too slow). I need to lock and unlock my Mac many times during the day so I was looking for a quicker way to get around this, but the app makes the entire unlock process much longer. On top of that, my phone’s battery life is worse because I’m constantly turning it on to do all the above where previously I didn’t. I have it always paired with my Pebble smart watch which doesn’t have these same connection issues. I’m not too bothered about spending $4 for the app, but I just wish it worked a bit better. The video and review are definitely misleading.


  34. ever since i got this app on my mac my wifi has been horribly slow


  35. That is certainly a needy and sensitive little app. It works on and off and then with all issues mentioned. But I work a lot in shared spaces and like the concept. So I just look forward to the time when it has come out of beta testing and my 4 dollar stake in the startup is paying off…


  36. – Does not work when you have a screensaver on your mac.
    – Does not find the mac anymore when you have been away for a long time.
    – I should have bought coffee with this money.