Welcome to another T-Rex talk. We're outside today and I want to be talking about GPS devices, but also how GPS actually works for a number of reasons.

But part of it is a few weeks ago I was posting on Instagram and posting about some Garmin devices, specifically some Garmin watches, and people had a number of different

opinions on the practical value and weaknesses of GPS, some of which were rather ill-founded,

which I'll get to in a little bit. So I think that all of us should have a pretty good

understanding of how GPS works, strengths, weaknesses, and the practical uses

of specific devices and an understanding of how far you can actually trust GPS, which means

we're going to get to talk about the weaknesses of the system. We're going to talk about how easy

it is to jam GPS, how easy it is to spoof GPS. I'll tell you right now, spoiler alert,

it's pretty easy. I myself was able to spoof some GPS devices,

which I did in a completely legal way,

didn't cause any interference for anybody.

I'll just say that right up front.

But I'll talk a little bit more about that later on.

So talking about GPS and how it works, so there are at any given time, just over 30 GPS

satellites above the Earth, and they last about 10 years.

After about 10 years, they fall out of orbit, and they have to send new ones up.

First GPS satellite was launched in 1978, and where those GPS satellites sit

is about 12,500 miles away from the Earth itself. So that is very far away. The Earth's diameter is

8,000 miles. So imagine that there is room for like one and a half Earths in between each of these satellites and the surface of the planet that we are walking on right now.

Because those satellites are so far away, those 30 satellites can see all of the Earth.

And from anywhere on Earth, you can see an awful lot of those 30 satellites.

And they are constantly broadcasting signals.

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