Crib pooper

This may sound a little odd. But I cannot tell when my child has pooped when he’s in his crib. Today I put him down for his nap and he cried for a solid hour. I checked on him twice in 20 minute intervals and I checked his diaper both times and there was no poop. There was a moment of 30 minutes where he was just playing in his crib but not crying, so I let him be.  then he whined a little bit and finally laid down. So I went to his room to move his stuffed animal and I could smell that he had pooped.  and I feel bad because I don’t want him to go to sleep in a dirty diaper but he doesn’t give me any indication that he has pooped or that he’s dirty. and since he’s finally down for his first nap I don’t want to wake him up. This has happened 3 times already. Any advice?