After the health app improvements, the headline feature for watchOS 5 at WWDC was Walkie-Talkie, a new app that lets you send and receive quick voice messages with friends and family. Earlier today, I got a brief demo of the feature and was surprised to discover that it works a little differently than I expected.

What I expected was a sort of voice message feature: you record a quick message, send it, and your contact does the same and sends one back. But that’s not how Walkie-Talkie on the Apple Watch works at all. Instead, when you initiate a Walkie-Talkie chat, what you actually get is a real-time FaceTime Audio call that just happens to include push-to-talk (PTT) instead of a full-duplex audio call.

Here’s how it works:

You and your friend agree to become Walkie-Talkie buddies (my term, not Apple’s). One of you asks to start a Walkie-Talkie chat, and then the other agrees to be your pal. You open Walkie-Talkie and then tap a button to send a message. You then wait a short amount of time for the Walkie-Talkie session to start. It was somewhere between five and 10 seconds in the demo I saw. (Take note: it was an early prototype version of the app. I’m told that it’s not available in the first developer preview.) Once the call is connected, your friend hears a chime and then the message you sent. They can then tap a button on their watchface to reply instantly. Their reply is sent to you instantly, and you can then reply by tapping a button yourself.

The question I had is how was it so instantaneous? The answer is buried right there in the second bullet point. When you send a Walkie-Talkie message to a contact, what you’re actually doing is initiating a specialized FaceTime Audio call. It connects, and then you’re just talking to each other, but instead of a real-time phone call, you’re pressing a button to send messages back and forth.

If both stop sending messages, it eventually ends the “call.” Right now, that timeout is about five minutes, but Apple is still tweaking the timing.

Why does this matter? Maybe it doesn’t, but I find it fascinating. This clever hack gives Apple a bunch of advantages. It ensures a real-time communication feeling to Walkie-Talkie chats. It’s way simpler than previous cellular PTT solutions like those old Nextel phones, iDEN, and its successors. And because it’s based on Apple’s own FaceTime instead of cellular numbers, it works equally well over Wi-Fi and cellular. (Interestingly, it doesn’t require iMessage to work; it’s a separate protocol.)

But it also has downsides, too. With Walkie-Talkie, you essentially are starting a real-time audio channel with somebody who just happens to be muted by default until you hit the PTT button. That means that it may drain more battery than just slinging voice memos at each other. If you initiate a Walkie-Talkie chat, you have to wait a tick or three longer than you might expect — though for your recipient, it’s instantaneous.

What I saw was an early version, and to my mind, it’s not quite ready. That’s mainly because the controls for what you’ll receive are pretty spartan. There’s only a toggle switch for availability. If it’s on, anybody who has agreed to be Walkie-Talkie buddies with you can send you a message that your Watch will play out loud. If it’s off, you won’t hear the message.

As much as I trust my closest friends and family, I don’t know that I trust them so far as to allow them to make my Watch squawk out any message they choose anywhere I happen to be. Hopefully the shipping version will allow more granular controls — something like being able to choose how that first message will arrive. I can’t expect my Walkie-Talkie buddies to always know whether it’s safe to send a message (but I can expect some of them to abuse that privilege of making my Watch say things at inopportune moments).

Though I don’t love the implementation right now, what’s perhaps most fascinating about Apple’s solution is that it’s a clever way to finally ship a feature that was originally promised at the launch of the first Apple Watch back in 2014. Promises to ship a Walkie-Talkie feature fell by the wayside in the company’s rebooting of the platform, but now it’s here. It's just here in a different way than old-school cellphone users might have expected.