Colorado requirements for smoke and carbon monoxide alarms??

[Sara Valentine]

I am installing wireless, ten year lithium battery combo smoke and carbon monoxide alarms in my rentals. 

I do not want the hardwired combo (more expensive and complicated to install) - From what I've read, hardwiring is required for multi-family housing, but I don't see that it is for single family residential. I have a single fam rental and also a duplex rental. I don't think the duplex would be considered multi-fam, whereas a 4 plex is? 

Also, apart from hardwired vs wireless, I still have the option of alarms in different rooms being interconnected (i.e. if one alarm goes off, they go off all over the house). I'm wondering if there are specific requirements for rentals in Colorado for interconnected alarms? 

If anyone has further clarity on what is required by law, please share. 

Kidde alarms are more expensive than other brands. Are they worth the additional expense?

THANKS in advance for any input!