Hardware wallet security question

[hatrabbit]

I have heard that people with hardware wallets such as the Nano S are safe in using them as hot wallets was well as for long term storage.  Is this true, and if so, how?  As I understand it, the security of an offline wallet is in the fact that the secret is never issued to any outside computer, ever. 
I store XRP using a utility called Minimalist Ripple Client, which generates key pairs and encrypts the secret with a passphrase.  If I wanted to I could open that utility on an online computer, enter the passphrase and do transactions without ever entering my actual secret.  But even though I'm entering the encryption key, isn't the original secret what is being sent to the blockchain?  For this reason I am of the belief that cold wallets should be loaded once and left alone until you're ready to empty them. 
So, if there is something about hardware wallets that gets around this constraint, could someone please explain it?
Thanks.

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[HeRetiK]

Hardware wallets store your private keys on a section of a flash memory card that can not be accessed by your PC.

When connecting a hardware wallet to your PC, all your PC does is communicate with the firmware of the hardware wallet, without even being aware of the data behind it. Whenever you send a transaction using a hardware wallet, all it does is return the signed transaction when requested, without the private key ever touching your operating system.

So basically a hardware wallet is like a tiny, airgapped, highly secured PC.