Fault tolerance

1. Power Failure - Have the computer or network device running on a UPS. If a computer, setup the UPS to properly turn off the computer after a few minutes if the power is not restored to help prevent the computer from data corruption. Another good idea, if available, is to have system messages sent to all network users or the administrators letting them know about the power failure and/or that the computer is being shutdown because of the power failure.
2. Power Surge - If no UPS is connected to the computer or the UPS does not provide surge protection, a surge protector connected to the computer or network device would help prevent the device from failing in the event of a power surge.
3. Data loss - Run backups daily or at least monthly on the computer if important information is stored on it. Create a mirror of the data on an alternate location.
4. Device / Computer failure - Have a second device, computer and/or computer components available in the event of failure to prevent a long down time.
5. Unauthorized access - If connected to a network, setup a firewall. Frequently check for updates for the device and/or computer operating system, lock device or password protect the computer when not in use, and store the computer or network device in secure area or area that can be locked. 
6. Overload - Setup an alternate computer or network device that can used as an alternative access point or can share the load either through a load balancing or round robin setup.
7. Virus - Make sure the computer has updated virus definitions.

Also see: Error, Fault, Network definitions, Overload