I've been intrigued by the new Handoff capability in iOS 8 and OS X Yosemite since I saw it demoed in June at Apple's Worldwide Developers Conference. It's a brilliant idea: Let apps notice when they're running on another device you're using and offer to transfer the activity to them. For example: Entering an email on your Phone? Your Mac or iPad can pick up the email you're working on, so you can finish on a larger screen and keyboard.

But what's it like in practice? Now that iOS 8 is shipping and I have several devices compatible with Handoff, I've been seeing what it can do. The quick answer: When it works, it's great, but there aren't enough apps to take full advantage of it yet. Also, it seems flaky on OS X.

First, you should know what is compatible with Handoff:

iOS devices with a Lightning connector along with 2012-or-later Mac models support Handoff. Both have the radio chips that support both Bluetooth Low Energy and Wi-Fi Direct.

If your device is compatible, you enable Handoff in the General system preference on your Mac and General pane of the Settings app in iOS; in both cases, look for an option that includes the word "Handoff."

All the devices have to be signed into the same iCloud account -- Handoff doesn't work with other users. (That's what AirDrop is for.)

Finally, make sure both Bluetooth and Wi-Fi are turned on for all devices.

Right now, the apps that work with Handoff are Mail, Calendar, Messages, Notes, Reminders, Maps, Safari -- all from Apple -- and the third-party GoodReader. (If there are others, I haven't found them.) [Oct 16 update: Apple Keynote, Numbers, and Pages now support Handoff.]

Using Handoff is easy enough: Open a compatible app one on device, and a few seconds later any compatible devices within Bluetooth range detect that it's running and offer to pick up the activity, if they have the same app. The offer is subtle: The app's icon appears in the lower-left corner of the lock screen or on the left side of the App Switcher (double-press the Home button to open the App Switcher, then swipe left).

iOS 8's Handoff feature shows apps available for handing off their activity in the left side of the App Switcher (left) and the bottom left of the lock screen (right).

The Handoff feature in OS X Yosemite -- when it works -- shows the available app on the left side of the Dock.

In iOS, Handoff works great. The icon appears within seconds, and the handoff is fast. Although you need Wi-Fi turned on, you don't need a Wi-Fi network. After the devices handshake via Bluetooth, the actual transfer happens over a Wi-Fi Direct connection between the devices -- no router or access point. I could hand off work when my iPhone and iPad were on the same Wi-Fi network, on different networks, and when there were no networks around (such as on my train ride).

Note that I couldn't always hand off data when there was no Wi-Fi network nearby -- sometimes I got error messages after the Bluetooth part was complete. But it worked most of the time in such networkless environments, and it always worked when I had a Wi-Fi network connection.

This means you can work on, say, a long email or detailed set of notes on your iPad and use Handoff to send that information to your iPhone, which then transmits via a cellular Internet connection. Or you could send a live map or Web page from your iPhone to your non-cellular iPad. It's like on-demand tethering without a carrier tethering plan.

But in OS X Yosemite's public beta, Handoff is balky, rarely working. It rarely sees Handoff apps running on iOS devices, and they rarely see Handoff apps running in OS X -- I've succeeded in making it work only a handful of times. We'll see if Handoff works as smoothly in the final version of OS X Yosemite -- likely to ship in a couple weeks -- as it does in iOS 8.

And Handoff would be even more useful if apps like iWorks and Microsoft Office adopt it. I suspect Apple will Handoff-enable iWork quickly after OS X Yosemite's release, but it's probably a hard sell for Microsoft, which really wants you to use its operating systems instead.

I recognize that passing documents over a direct handoff can lead to duplicate files. That's an issue with iWork, though not with server-based apps like Reminders or Mail, or with snippet-based apps like Safari and Maps. For document-oriented apps like iWork or iMovie, Handoff would need to coordinate with iCloud Drive to use the cloud master file if available, and reconcile the local versions if there's no Internet connection available to connect to iCloud. iCloud Drive does that anyhow behind the scenes, so as long as iCloud Drive knows which version is latest, this Handoff/iCloud cooperation should work.

Anyhow, I really like Handoff: It's brought a convenience I didn't know I wanted. Now I want more.