I would consider chipping anyway - as an indoor cat IF he get out accidently he is much more likely to not know how to get home - he won't kno the geography of the area or know the smells. I have heard to a breeder who was burgled and the cats let out - if they had been chipped she wold have seen them again! My birman is chipped for this very reason - I can trust my family to be careful with doors but other people just don't think somtimes and other people's kids are worse - one child let the cat out and the mother said (after a 10 min chase afound the block to get the cat back in) 'oh, when you said don't let the cat out I didn't think you meant it!' ?????????
It doesn't cost that much and is worth the peace of mind.