Spoilers below if you haven't read the article:
1. The key shouldn't be kept in the closet outside the safe
2. Opening the door should force the magnetic sensor to be triped, the door must be in the way of the sensor. Additionally, why was the sensor on the outside of the door?
3. The combination lock should have a viewing angle that requires the user to block any cameras.
4. You need human patrols.
5. Sensors should be independent; the heat/motion sensor shouldn't both need to be tripped.
6. They needed sensors that could not be easily seen or detected by someone in the safe (hidden cameras, sensors embedded in another object).
7. The needed multiple sensors instead of one each.
8. The sensors should adjust the current flowing through them so that the wires can't be bridged, and the wires shouldn't be exposed.
9. There needs to be a random factor inserted such as random patrols, a sensor that moves in a random way, the combination is changed randomly.
10. They should have a time control on the safe that only allows it to be opened during certain times. There could be an override, but it'd be it should be difficult and rarely used (hard to copy).
Just a few off the top of my head, more cameras would also be good -- what else did they do wrong?