The Garmin 405 is a wrist-top GPS receiver. There's a very good explanation of how GPS works on Garmin's website. Basically, a GPS receiver works by locating and receiving transmitted signals from four or more of the 24 GPS satellites that are orbiting the earth. The GPS receiver compares the time the signal was transmitted to the time the signal was received to determine the distance from the receiver to the satellite. This information can be combined with the information from other satellites to estimate the location of the receiver. By comparing multiple signals over time, the GPS receiver can determine how far you've gone, and this information can then be used to determine your pace.
The Garmin 405 is split into three screens that can be set to display whatever you deem important. I currently have mine set to time, distance, and instantaneous pace (the default when you get the watch...I don't have the heart rate monitor version and can't think of anything that would be more useful anyway). It's controlled primarily by the bezel that surrounds the face of the watch, though it also has a start/stop and lap button. Anyone who's used an iPod Classic knows how the bezel works, as it's operated by touch. It can also be wirelessly synced with your computer, and you can analyze your run data and/or upload it to any Garmin compatible training log.
The Garmin 405 is a lot nicer looking than the old 205 and 305, though it's still a big and bulky watch. It might look alright on a large man's wrist, but it's not something that a small woman would want to use as a regular watch. Additionally, the plastic immediately above and below the watch's face is hard and will not bend around your wrist. Clearly, this watch is a training tool, not a fashion accessory. Don't buy it expecting to wear it around as an every day watch. Buy it intending to put it on to run and take it off when the run is over.
|Garmin 405 compared to a Nike Triax Fury, which is also a fairly large watch.|
|GPS units measure secants between points. The black line represents the path run, while the red line represents the path the GPS measured.|
My biggest complaint about the 405 is the fact that it is not waterproof at all. The website claims that the 405 is "water resistant," but I'm pretty sure that means that water won't get inside the watch and break it, not that it functions properly if it gets wet. The tiniest bit of sweat or rain will cause the bezel to go haywire. If you remembered to lock the bezel beforehand, you'll be fine. However, if you forgot to lock the bezel, it will start beeping wildly and will scroll through screens (and Murphy's Law says it will get stuck on the useless virtual partner screen, and the wet bezel will not allow you to change it back to a useful screen). The new Forerunner 410 is supposed to fix this problem, but I have not had an opportunity to try it out. The other possible concern is that the 405 has a relatively short battery life (8 hours in training mode), so you really have to remember to charge it often.
The Garmin watches are one of those things that once you have, you wonder how you ever ran without. I've found that it's an indispensable training tool for tempo runs and other long interval workouts, as well as for measuring distance on long runs. However, I'd caution you not to let it tempt you to run your easy runs too hard, which can lead to compromised quality workouts. I leave mine at home on easy and recovery days. Finally, the 405 is a very complex watch with tons of features. I've found that only a few of them are useful to me. Depending on which features you think you'll use the most, you may be able to get away with a less expensive Forerunner 110 or 210. However, they really are not that much cheaper, and many people will recommend you spend the extra $50 and get a "real" Forerunner.
This may seem obvious, but I'm going to point it out anyway, just because I read the best running store stories thread on LetsRun. GPS watches only work outside. They will not be able to receive the satellite's signal on an indoor track, and they certainly will not work on a treadmill, since not only are you inside where the signal can't reach you, but your location is not actually changing. However, you can purchase an optional foot pod, sold separately, for indoor use.
The Garmin Forerunner 405 retails for $249.99 for the non-heart rate version and $299.99 for the version with the heart rate monitor. It is available from Garmin's website, as well as many running stores, including The National Running Center. The new Garmin Forerunner 410 retails for $324.99 for the non-heart rate version and $374.99 for the version with the heart rate monitor. The 410 is also available from Garmin's website and from many running stores.
Full disclosure: I bought this myself, and I'm pretty sure I paid full price, so nothing to disclose here.