Autonomous bots have pre-programmed navigation strategies and don't rely on humans to get around. We often use several proximity sensors ( like these from pololu ). The positioning and interaction between the proximity sensors is what leads to the navigational behavior. For example, the cliff avoider bot has two proximity sensors each positioned in front of the two main wheels. If both proximity sensors detect something then the bot goes straight- it assumes it is not near an edge. If either proximity sensor stops detecting ground the bot fears a cliff and turns in the opposite direction. These simple rules lead to a bot that seems to follow the perimeter of convex shapes. This perimeter following is a more sophisticated behavior than any of the indiividual rules from which it emerges.