iOS 4 spotlight: iPod touch Wi-Fi stays connected when asleep -- iPhone too?

iOS 4 on iPod touch persistent Wi-Fi connectivity

One of the more interesting notes on Apple's iOS 4 for iPod touch page is persistent Wi-Fi connectivity, so Skype calls or push-notifications can come through even when your iPod touch is in sleep mode:

iPod touch can stay connected to Wi-Fi when asleep so you can receive incoming VoIP calls and notifications from compatible third-party apps.

There's no word on whether this applies to the iPhone as well (since cellular data is typically persistent anyway), but it would be a nice feature to have in all iOS devices -- including iPad, especially when roaming with data turned off, or even just to prevent the delays that usually accompany reconnecting to Wi-Fi based remote control apps.

For more on Apple's latest software, see our complete iOS 4 feature walkthrough...

[Apple iPod touch iOS 4 page]

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Rene Ritchie

Editor-in-Chief of iMore, co-host of Iterate, Debug, Review, Vector, and MacBreak Weekly podcasts. Cook, grappler, photon wrangler. Follow him on Twitter and Google+.

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Reader comments

iOS 4 spotlight: iPod touch Wi-Fi stays connected when asleep -- iPhone too?

46 Comments

This just makes me imagine a mophie juice-pack-air type cover accessory with a ear-peice & mic for the iPod Touch. Am I alone ?

I hope it's an optional extra, not something enforced. I like my wifi sleeping when the phone is.

this does happen on iOS 4 i have it installed on my phone and the wifi does stay on in sleep mode

@Matt:
Wifi takes less power than 3G. By quite a bit.
If you have wifi, you want the phone to maintain all its data connections on the wifi, and drop to edge (2g) for incoming calls.
With more and more push enabled apps, (not to mention data caps) its more battery friendly and more important $ wise to stay on wifi, and keep those power hungry 3G radios off.

This is great! The biggest way this bugs me is with Apple's remote app, which only works over WiFi. It's so annoying for it to have to reconnect everytime I use it when I pull it out if sleep. This will be very nice.

@frank:

this does happen on iOS 4 i have it installed on my phone and the wifi does stay on in sleep mode

Wifi says on in OS 3.2 as well, but only if you are plugged in.
Soon as you unplug it drops wifi within 10 seconds.
So if you tested plugged in, the jury is still out.

This will be key to making the next iPod touch work for facetime. I'll be buying two iPods for my family if the next one has a front camera.

I like to think as my iPhone as being like a sever is has 2 network connections teamed together making it data redundant.

@icebike
Interesting! My signal is not exactly amazing where I live, so i'm generally switching the wifi on and off all the time. Is it better to just tell the phone to not bother with 3G and leave the wifi on when i'm at home?

@Matt:
Just turn both on, and the phone will handle it the way it was designed. You are home. You have outlets, don't worry about battery.
Of course this won't matter till iOS4 is out, because the current OS drops wifi fairly quickly when sleeping, (unless plugged in).

Doesn't look like it works for the 3GS on iOS 4. Sometimes I hit the home button on when the phone is locked and I see 3G for a few seconds then it goes back to WIFI. Other times it seems like it stayed connected.

Yeah, I've noticed this working pretty well with notifications while my iPod Touch 2G with iOS 4 is sitting on my table.

@icebike: I thought WiFi was only more power efficient based on how much data is transferred (watts per byte if you like), but when idle I thought 3G was much more power efficient since it practically turns off, no?

This would be great if it were to work on the iPhone as well. Ever since the introduction of the capped plans by AT&T a lot of iPhone users have scrutinized their wireless bills and have noticed that there are data charges in the middle of the night and one theory is that Push enabled features are running on 3G/Edge in the middle of the night and racking up charges that prior to the capped plans being introduced were never even noticed by most of us. There is a growing thread at Apple Discussion board (http://discussions.apple.com/thread.jspa?threadID=2450738&start=0&tstart=0) of people trying to figure this out. So having WiFi be a persistent connection at night might help if some of the theories are true.

This little feature makes the iPhone as Remote actually useful.
Now, 0 delay when picking up the remote, swiping to unlock and pressing the TiVo 30 second skip button.

Did apple give an APIs for Wifi in this latest update, ? would be great to choose where your Wifi was on & off depending on your location. I only ever use wifi in a couple of places and don't need it the rest of the time.

MrC:
Who has an iPhone and no email checking, no push apps?
A radio that has to broadcast 30 feet is going to take way less power than one that has to broadcast 5 of 10 miles.
Most WIFI, transmissions are listen only. There is not that much traffic from the client to the access point, certainly less then the with 3G.
See also http://tinyurl.com/l2ajn7

What would be really useful (in terms of ipod parity) is soft gps via wifi.
I would love to not have to turn on the battery-sucking gps radio when all i might actually need is just "good enough" gps.

iPhone (iOS4 GM) too stays connected when asleep (verified) ;) , but yet no 3º party apps in app store for try it in background.

I have an IPod Touch 3G with the iOS 4 GM in it, and I can say it stays connected on Wifi.
I didn't notice my battery draining any quicker and it's always nice to receive push notifications and email almost instantaneously, so thumbs up for Apple.

That would be fantastic! On a recent trip to Vegas I made sure we had a hotel with free wifi and that I also had a data roaming plan.
To my surprise, the iPhone leaks about 10MB of data per night because even though you have wifi available, when the phone goes to sleep it switches to 3g for checking email, voicemail, and push notifications.
That works out to about $3 per night. Without a roaming plan about $30 per night. All when it should have been using wifi!

@icebike: My point was that even when no data is being trasnmitted, WiFi radios are not turned off, they just go into a semi-low power mode, otherwise the access point would immediately decide the device has disconnected and disassociate.
Whereas with 3G/GSM even when maintaining a data connection, if no data is being transmitted the radio basically turns off and only wakes up periodically to let the cell tower know you are still in range.
I would imagine even with Push, email polling and a VoIP app running, the data connection would be idle most of the time while your phone is asleep so 3G would still be more power efficient in theory.

@icebike: Oh and the link you provided is correct, but that only applies to when data is actively being transmitted since they're talking about using data services on current iPhones that turn off WiFi when asleep.

Actually this feature is already on the iPhone (3.1.3) and the iPad (3.2), put to sleep your iPad and still you will receive mails.

@MrC:
That waking up periodically amounts to every millisecond IIRC.
Even for mail checks on a half hour schedule it has to wake up the transmitter, log into the tower, establish a TCP connection, check mail, transfer mail, etc. All of this takes much longer on 3G, a more battery demanding radio than the fast but whimpy WiFi.
I didn't make this up. Its widely established that keeping wifi on in sleep mode is more battery conserving than staying on 3G for the normal mix of traffic on a smart phone.
This is why Android has a WiFi Sleep policy of NEVER as the recommended setting for users with wifi available most of the time.
3G being a power adaptive technology, living very close to a 3G tower might make 3G a better way to go.
But most people with a phone that can do this actually get better runtime with WIFI enabled and Never Sleep selected. Usually by quite a lot.
(Part of this is because the iPhone is continuously getting a new IP via 3G. Some studies suggest every minute or two.http://research.microsoft.com/en-us/um/people/maheshba/papers/ephemera-i...
For those interested: The only way you can reliably know if your phone drops WiFi when in sleep mode is to look up its IP in settings, and ping the phone from some other computer. Let it fall asleep (not plugged in), and your pings will fail 10 seconds after it goes to sleep. With iOS4 (or an Android phone) you can ping it on wifi forever.

Yes this is kind of an option you have to turn on notifications for this to work if they're off then wifi will disconnect

@ryan: yes, I think so too. The battery life of my iPod touch is now horrible with ios4! It's dead after one day in standby. I hope apple is going to fix this issue pretty soon.

I could have sworn my iPod kept wifi on while sleeping before ios4... And now that I have os4 the wifi ALWAYS disconnects when I un sleep it. It's really really annoying, especially because it has no reason to disconnect!

If you want to turn off persistent wi-fi on your iPod Touch just turn off all notifications and alerts in settings. If you have even one application with alerts/notification turned on it will turn on persistent wifi.

HJ, thanks for the tip. All these days I've been wondering why the wifi stayed on all the time.
In 38 comments, nobody has mentioned the battery impact of this feature. I charged my ipod in the morning, and the next morning I barely had any battery left. It happened twice, and I didnt know why. Now I know.

I am using iPod Touch 2G and installed iOS 4.0. I found my iPod Touch used up the battery in just half day comparing to a few days before. And the wifi connection is not stable. It reconnects to the base station every minute. I tried WPA2, WPA and WEP but no help. Would anyone tell me a better solution?

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My ipod touch gen 4 (iOS 4.2) just got this problem a while ago. It was fine for about 4 months after buying and now I have to keep it awake to continue downloading