There are three main types of radiation.

Alpha, which is a helium nucleus (2 protons, 2 neutrons) ejected from a nucleus at high speeds. These particles are so large that they only travel a few centimeters in air before they are blocked or absorbed. They are so weakly penetrating that they can't harm you from outside your body because they won't penetrate your outermost layer of skin. However, they are also extremely ionizing and can do 20 times the damage a gamma ray can do if the materials that emit them get inside your body. They are also the most difficult to detect of the three, and detecting them reliably requires specialized equipment like alpha-specific detection probes. Internally, it's the most dangerous to you, but externally it's the least.

Beta, is an electron that gets ejected from an atom at high speeds (can be close to the speed of light). These are more penetrating than alpha, but can be stopped by thin sheets of metal, sheets of plastic, or acrylic. They are a little more hazardous if the materials that emit them get on your skin because the beta particles can penetrate far enough into your skin to cause burns. Inside your body, they do about the same amount of damage as gamma rays. They can usually be detected by most of the same equipment that can detect gamma radiation.

One common misconception I want to address about alpha and beta particles is some people think those particles float around like dust and are being filtered out by masks or filters. That's not the case. They're not the thing floating around (if that's even happening). They are ejected from the nucleus of an atom at such high speed, they don't have time to "float" anywhere before they hit another atom.

Finally, gamma rays are what most people think of when they think of radiation. They're electromagnetic energy, similar to light and they're the most penetrating. X-rays and gamma rays are very similar. X-rays are emitted by the electrons, and gamma radiation is emitted from the nucleus. Gamma radiation is also shorter wavelength, and usually stronger. Because its ability to penetrate materials, gamma radiation is very easy to detect, but that also makes it very hard to shield against. So it requires a considerable amount of dense material (soil, concrete, metal, etc) to shield against gamma radiation.

So those are your 3 main types of radiation. I'm not covering neutron radiation (which is probably the worst) because it's generally only present close in to a nuclear detonation or an operating nuclear reactor. And if you're in either of those places... probably isn't much you can do about protecting yourself.

As far as devices, in my opinion, the most important device to have is something to monitor ambient radiation intensity, and track your dose. Something like this: https://www.ebay.com/itm/365774270357 I'm not endorsing that or any other seller, just providing information.

To be honest, you don't need alpha detection because the likelihood that you will encounter a sole-alpha emitter in a situation that will require you to measure and manage it is so remote it's not worth considering. Basically, you would only encounter it in a dirty bomb scenario, and such a scenario isn't likely to bring prevent the government and emergency responders from managing it. To be honest, if you're running around an RDD hotzone with your own equipment and aren't part of the response, you're going to get yelled at, possibly arrested.

In a nuclear detonation scenario, nuclear fission fallout is a mixture of dozens of elements, and there are always some gamma emitters present. So for nuclear detonation, you only really need gamma detection capability.

Now, that said, if you insist on alpha/beta/gamma contamination detection (this is waving a wand or probe over things to see if they're contaminated), I'd consider this combination of devices: https://www.ebay.com/sch/i.html?_nkw=Ludlum+model+3+44-9

These devices aren't used to tell you how much radiation is around you or track your exposure. That's what the other device is for.

If you've made it this far, I have one more thing to tell you, and you probably won't like it. These devices aren't magic boxes. And I can't simply say to you, "buy this, keep the number under this, and you'll be fine." If it were that easy, I wouldn't be doing what I do. So there's some education you'll need to do, and to help with that, I wrote this post a while back to help people find the necessary resources to educate themselves, because you can buy the most expensive tool on the planet, but it won't do you any good if you don't understand and know how to use it.

PSA: Don't Ask "What Geiger Counter Should I Buy?" until you've read this post.