To have wi-fi "on" all the time involves very little radiation. GSM is much more, and it keeps talking (waking up) all the time, which is what you hear if you leave a phone near a computer with a sound system, or near a TV.

wi-fi (normally) uses automatic power saving mode, which means that a) when it's idle it isn't really radiating, (and when it transmits it'll send the data in bursts btw), and b) it's using very little battery.

However, some (as in 'a few') wireless routers are unable to support power saving mode, if your AP is one of those then you'll experience serious battery drain when connected. With a normal, good wi-fi router my N800 can stay online 2-3 days (or it could, when the original battery was still fresh), but with a bad router it would drain in 2-3 hours. In both cases this would be with gmail notification running, email running (and polling), skype running and connected, rss application running.

i just had the n900.
i have the same problem
on my n95, when an app needs internet, it will ask which accesspoint to use. after i'm finished with the app and close it, it will close down the internet connection.

the n900 doesn't do this. if you turn it on once, even through any app that uses it, the connection will stay on unless you turn it off manually.

can this be controlled?

I am also a little concerned regarding this matter.

If we had something like the Nokia Energy Profiler for S60, we could prove that / how much power it drains. I really loved that tool

Is there anything alike, can it be made?

Thanks,
Corwin

There is Battery Eye and BatteryGraph. Both available in the maemo repositoris. I think extras-devel.

Especially BatteryGraph shows network connection, charging and the like very nice...

There is an application "autodisconnect" which disconnects you from gprs and/or wlan if no data is transfered.

Yes - using this application and 30min-email-sync is functional (I'm using it).

The battery drain for always connected 3g-dataline is horrible.

Does your Email app automatically connect to the internet when no connection is opened ?
Cause I need to set "search every 30 mins". If not, it won't sync my Emails.

Yes it does. But I sync every 60mins.

Do you mean that constant data transfer on background depletes battery? Or do you meant that even plain 3g connection without data transfer is CONSIDERABLY more power hungry compared to 2g connection.

I don't know if there is a difference between connected 3g or 2g (but I think 3g is more expensive). But I know there is _quite_ a difference between "no connection" and "3g connection".
Can't say how much data is transfered. But it's not that much (15mins email-check, skype and sip only connected - I tested this "scenario" a couple of days ago, since then I switched to autodisconnect and sync every 60mins).

I can have the N900 continuously connected to 3G for more than 2 days if there is very little actual data transfer (and I do have mail checking set to every 30 minutes). So either it's heavily network dependent or you have some widget/app transferring data very often.

Skype, SIP and IMs do relatively lot data transfer, so having those connected does not count as connection idling.

And when battery power consumption is relatively low, so is the total electromagnetic radiation output power of the device...