I'm not familiar with Amber, but I believe it is an app.
This is a physical device that holds your key and connects to the Internet via WiFi.
You can leave the signer at home and remote sign any event from anywhere.
Discussion
Can you recommend a self hosted signer? Fwiw amber is open source and runs on lineage, but remote signing sounds good for my iPhone.
Remote signing is a great concept, but not many clients support it right now.
If you want to play with remote signing, then this is the device I'm using:
https://shop.lnbits.com/product/nsec-remote-nostr-signer
My daily driver, however is getalby.com which I use for desktops.
I'm mostly iPhone, which has limited options, but this is the one most people use: