Sentimental Value is a secret achievement/trophy in Deus Ex: Human Revolution. It is earned by keeping Megan Reed's bracelet you find in the evidence storage for yourself instead of giving it to her mother, Cassandra Reed.
During the quest Motherly Ties, if the player hacks the safe inside the evidence storage locker in the alley just outside the Detroit Police Station near where you meet up with Jack O'Malley during Cloak & Daggers, they will find Megan Reed's bracelet. The safe has a level 3 security lock on it. You can either hack it for 75 experience points or enter the code 7196.
When you turn in the quest, you will be given two dialogue choices. While giving it to her mother will reward the player with the same amount of experience points (1000), taking it for themselves and lying to her mother will give them this achievement.