The Sapper, mentioned in the Sentry Gun Operational Guide as the FM/AM Ultra-Sapper, is the default Building weapon for the Spy. It is a small box inscribed 'ELECTRO-SAPPER' and sports a dial and switches. It also features two clamps that are deployed when used. This weapon, when placed on a enemy building will "sap" away 25 health per second. After this, the building explodes into gibs and the sapper dissapears. This can be taken off a building by any two hits of a Wrench or one hit of a Homewrecker or two with the Neon Annihilator. This, when taken off a building explodes into two parts, which give 3 metal each and/or 1 unit of ammo. The spy has infinite sappers and places them as fast as the user can click.
- Inverting the model in first-person view (to make the characters look like they are left-handed) will also invert the writing on the Sapper, obviously making it read 'REPPAS-ORTCELE'.