I’ve written before about how easily data use on a mobile Wi-Fi hotspot can creep up on you, particularly when you’re out and about with a laptop.

The culprits, of course, can be many—anything from system updates quietly downloading in the background to giant file attachments fetched by your email client.

But while there are plenty of ways to prevent your laptop from going nuts with your mobile hotspot, there’s nothing like a real-time bandwidth gauge to tell you whether you’re burning through mobile data at a too-furious rate.

Bandwidth+ monthly preferences

You can set Bandwidth+ to track your monthly data usage, handy for checking whether you’re approaching your cellular data limit for the month.

Now, the Mac’s own Activity Monitor (just do a Spotlight search for “Activity Monitor”) has a “Network” tab that’ll give you a detailed breakdown of how much data your various apps have used since the last time you booted your system.

All well and good, but I prefer something a little more simple: namely, a bandwidth gauge that sits right at the top of my MacBook Air’s desktop, perfect for warning me of any data hogs on my system.

The app I’m currently using is Bandwidth+, and it’s free for download from the Mac App Store.

Once you launch it, Bandwidth+ puts a bandwidth meter in the top-right corner of your desktop, right next to the system clock and your other Mac notification icons.

The meter itself simply tells you how much bandwidth you’ve used on a given day and for a given hotspot—meaning, for example, that Bandwidth+ can keep track of your data usage for your home network, your mobile hotspot, and any other connected Wi-Fi networks.

You can also set Bandwidth+ to track your monthly mobile usage, handy for checking whether you’re approaching your cellular data limit for the month. (Of course, Bandwidth+’s monthly tally doesn’t account for the mobile data your other mobile devices have used, such as your smartphone and tablets.)

But while Bandwidth+’s monthly data-tracking features are certainly interesting, I mainly use it to keep an eye on my mobile data use for a single sitting.

In other words, if Bandwidth+ tells me I’ve used a gigabyte of data before I’ve finished a cup of tea, I know something’s amiss—and I can shut down my Wi-Fi hotspot to look for data hogs before wasthing any more mobile data.

Download: Bandwidth+

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Note: The makers of Bandwidth+ haven’t compensated me in any way for this article.