user-1: This question is about how standalone a hardware wallet (such as Trezor) is. Or in other words, what other components, if any, does it depend on.
So this is about what other components are needed for the Bitcoins to end in Bobs hardware wallet when Alice wants to send Bitcoins to Bobs wallet address.
So for example, is a hardware wallet dependent on connecting to either

some software with the wallet address that runs on the PC and
connects to the internet, or
some web application, or maybe a part of the BTC ecosystem, that
hosts the wallet address

Or is it possible to send Bitcoin directly to a hardware wallet (such as Trezor) simply by plugging the hardware wallet to a USB port on your PC?

user121614: A hardware wallet such as Trezor is simply a clever storage of your private keys that can be made to do some things defined by its firmware (like signing a transaction). The instructions to do these are relayed to it over USB from any device running software capable of producing them. Usually this will be a PC or a phone running wallet software created either by the manufacturer or the open source community.
I will try to outline what exactly is needed for Alice to send some bitcoin to Bob when they are both using a hardware wallet:

Bob needs a bitcoin address to give to Alice. He uses his wallet software to instruct his hardware wallet to generate a new address from its extended public key. This step could be done without internet connection, however without connecting to the Bitcoin network the wallet software wouldn't know which addresses have already been used and might end up reusing an address. Bob looks at the generated address on the hardware wallet display (not on his PC because it might be infected to show an attacker's address instead) and gives it to Alice.

Alice uses her wallet software to create a transaction, entering Bob's address, amount to send and tx fee (potentionally more, like RBF, locktime...). She needs to connect to the Bitcoin network for this to know her UTXOs. Once created, she sends the unsigned transaction to her hardware wallet for signing. The hardware wallet will show on its display the transaction's details and asks her to confirm it. The signed transaction is then sent back to the wallet software and can be, now or at any point in the future, broadcasted to the Bitcoin network.


TL;DR: You need a PC or a phone running wallet software to use your hardware wallet.

-1: <p>This question is about how standalone a hardware wallet (such as Trezor) is. Or in other words, what other components, if any, does it depend on.</p>
<p>So this is about what other components are needed for the Bitcoins to end in Bobs hardware wallet when Alice wants to send Bitcoins to Bobs wallet address.</p>
<p>So for example, is a hardware wallet dependent on connecting to either</p>
<ol>
<li>some software with the wallet address that runs on the PC and
connects to the internet, or</li>
<li>some web application, or maybe a part of the BTC ecosystem, that
hosts the wallet address</li>
</ol>
<p>Or is it possible to send Bitcoin directly to a hardware wallet (such as Trezor) simply by plugging the hardware wallet to a USB port on your PC?</p>
 121614: <p>A hardware wallet such as Trezor is simply a clever storage of your private keys that can be made to do some things defined by its firmware (like signing a transaction). The instructions to do these are relayed to it over USB from any device running software capable of producing them. Usually this will be a PC or a phone running wallet software created either by the manufacturer or the open source community.</p>
<p>I will try to outline what exactly is needed for Alice to send some bitcoin to Bob when they are both using a hardware wallet:</p>
<ol>
<li><p>Bob needs a bitcoin address to give to Alice. He uses his wallet software to instruct his hardware wallet to generate a new address from its extended public key. This step could be done without internet connection, however without connecting to the Bitcoin network the wallet software wouldn't know which addresses have already been used and might end up reusing an address. Bob looks at the generated address on the hardware wallet display (not on his PC because it might be infected to show an attacker's address instead) and gives it to Alice.</p>
</li>
<li><p>Alice uses her wallet software to create a transaction, entering Bob's address, amount to send and tx fee (potentionally more, like RBF, locktime...). She needs to connect to the Bitcoin network for this to know her UTXOs. Once created, she sends the unsigned transaction to her hardware wallet for signing. The hardware wallet will show on its display the transaction's details and asks her to confirm it. The signed transaction is then sent back to the wallet software and can be, now or at any point in the future, broadcasted to the Bitcoin network.</p>
</li>
</ol>
<p>TL;DR: You need a PC or a phone running wallet software to use your hardware wallet.</p>
