Garmin Forerunner 405CX Review

For the past year or so I’ve been using a heart rate monitor watch – a Polar F4 – when running. Despite a few really stupid flaws – most notably, it has no light, making it impossible to read if you run early or late in winter – this served me perfectly. After knackering my right IT band, though, I’ve found myself having to slowly build back up my distances from almost nothing – at its worst I could only just run 5k before my knee was in agony – so I decided to upgrade to a GPS watch that can accurately track pace and distance as well as time while I get back up to speed.

After having considered at least five different models and reading dozens of (sometimes useless) reviews, I chose a Garmin Forerunner 405CX*. Here’s what I’ve found since buying it that I wish I’d known beforehand.

One caveat: I don’t think it’s possible to properly review a device such as this without having used it for a few months, and preferably through winter. When buying a GPS watch there were several questions that I wanted the answers to, however, so I think it’s worth putting that information online now for anyone else in the same situation. I’ll update this a few months down the line.

What you get

It isn’t entirely clear what you get in the box with the 405CX before you buy, particularly as some Forerunner watches are sold with and without heart rate monitors. So, here it is: the standard 405CX package I bought includes the watch on a rubber strap, a heart rate chest strap, a small USB antenna for PC transfers, two velcro straps, a strap changing tool, a charger (it’s USB, with a USB mains adapter) and a quick start guide. The heart rate sensor is much the same size as the Polar T31, but has a battery that can be changed without the use of a stanley knife. The chest strap seems to be a little larger than a medium-sized Polar one.

What you don’t get

A manual, and god knows you’ll need one because the quick start guide covers just that: the start. Download the full manual in PDF here. Also, there are no instructions on how to change the strap – see the video here, but beware that it’s a far fiddlier process than the presenters make out. There’s no software CD, either – instead this must be downloaded from here.

Why so many wriststraps?

The 405CX looks more like a watch than some older Garmin models, but this is accomplished by building the GPS receiver into the top of the lower strap. It’s a clever design, as the receiver always points up when you run, but it makes the watch huge. If you have small wrists, like me, then the standard strap is uncomfortable, so switching to the velcro one is a must. Apparently these straps are not included with the cheaper 405 (non -CX) model. Here’s the watch on the small strap on my puny wrist – GPS receiver side facing the camera.

Using the watch

The 405CX has two buttons: one to start and stop, and one to lap. All other controls are on the “touch bezel” – the silver ring around the bezel that works rater like an iPod controller. Tapping and holding one of the four quadrants opens that function, scrolling a finger around adjusts values and single-tapping selects. It takes a few minutes to get the hang of, but works well. The bezel can be locked by pushing both physical buttons at once – I’ve heard that this is a must if running in the rain, but it’s no problem to lock every time.

GPS reception is impressive. It takes about a minute to position at the start of a run – go out, stretch, and it’ll be ready – and kept its grip on the satellites even in parts of my run that are under some fairly heavy tree cover.

The options available are numerous. At its simplest, you can run until you want to stop and the watch will track your time, pace, distance and heart rate. It’s simple to combine this with the Virtual Partner – set this to run at, say, 4:30 per km and it’ll track your progress against that standard through each kilometer. When running on streets rather than a track it’s handy to switch on the auto lap function that adds a lap marker every kilometer, mile or whatever – the watch beeps at each marker, and displays your pace through the previous lap.

More usefully for me, you can set the device to monitor you through a fixed run – for 45 minutes, say, or 10km – and alert you when it’s done. There are also modes for heart rate zone training and intervals (run, rest, run, rest, and so on). The Advanced workout option allows for even more complicated settings, but cannot be set up on the watch itself – these must be set on the PC and transferred.

By default the watch will show two screens of information when running: one for your heart rate, and another showing the pace and so on. Enabling the virtual partner adds a third. You switch between them by tapping the bezel when running, which isn’t as easy as pressing the physical buttons on my Polar, but there’s also an option to automatically cycle them at various speeds. It’s possible to completely customise what’s shown, too: there are three main screens available, each holding three variables, plus the heart rate screen, so you could have up to twelve figures on display should you wish. I’ve set it up with just one screen for time, distance and pace, and disabled the heart rate screen entirely (it’s still logged).

The watch is charged using a clip-on adapter, which is simple enough to use. At the moment it seems to lose approximately 10% of its charge per half-hour of running, so I’d bank on charging it once per week.

Oh, and it has a light. Thank god.

Viewing the data

After running you need to hold the reset button for two seconds to end the session and commit it to memory. Garmin offers two ways to track your runs: Garmin Training Center, which is PC-based, and Garmin Connect, which is online. I’ve only used Garmin Connect.

Synchronising the watch with the website is simple enough: plug in the USB stick and place the watch nearby and the two will detect and transfer the last run. Once transferred it’ll appear on Garmin Connect when you next log in. Here’s a snap of the main run screen (map obfuscated to hide my home address):

As you can see it plots a Google Map (with surprising accuracy – you can see which side of a narrow road you ran on, for instance), with pace, elevation and heart rate graphs below. Lap times and paces are shown to the left, along with lots of average data. Click Player and you get this screen:

.. which allows you to replay the run, or check out where you were when any strange peaks or troughs appear on the charts (hint: waiting to cross roads). It can only graph two variables at a time, though, so you can’t have pace versus elevation versus heart rate here. A report option allows you to tally data for a period (the last month, say), and you can set goals. These aren’t very sophisticated, so you’re limited to “run two hours this week” rather than “get back to 15km per run within two months”.


As I said earlier, time will tell. For the moment, though, the 405CX does everything I wanted it to, and a whole lot more that may or may not be useful in future, and the Garmin Connect website is particularly nifty. I’ll update this review in the depths of winter once I know how it copes with the cold and pouring rain. If you fancy buying one, please click here* – it’s £250 from Amazon, or about £300-350 elsewhere.

Update: Rain

One concern I had was whether the 405CX – and the bezel in particular – would cope with rain, as I’d read reports of it causing accidentally activating in the wet. Tonight I took it out for a run in some truly awful British weather, though – rain, wind, yuck – and it was fine. I left the bezel unlocked while it got a fix, with no problems, then locked it during the run. I got soaked, so did the watch, but it kept working with no problems.

* These are affiliate links, so if you click one I’ll get a small kickback to waste on comic books. The price you pay is the same, and Amazon is the cheapest place to buy (I shopped around quite a bit).

All © 2020 Tom Royal