The person who remembers a detail has made attention visible without announcing it.

Attention is invisible while it is happening. You cannot see someone listening, and claiming to have listened proves nothing, so the only real evidence arrives later, when a small fact you mentioned once comes back in their mouth. Nobody has to say they were paying attention; the detail says it for them.

Rather than telling people you care, keep the small things they tell you. The name of the dog, the week of the operation, the thing they were dreading. Bring one back into a conversation this week and watch what it does, which is usually more than a compliment would.