Whites XLT DFX MXT, many Minelabs, many Fishers, Tesoro Bandido, Lobo, Cortez, efx ground MX400, Treasure Commander TC2X, original Bounty Hunter Red Baron, and many more!
I must admit I never considered alleys as a possible place to detect, and I grew up in Phoenix and we always had alleys. Off the top of my head I would say you would likely just find junk, but who knows. As kids, we played in the alley often and where kids played you just might find stuff they lost.
I think alleys would be a good place to search but you will certainly be overwhelmed by trash. However, wherever there are kids and riff raff you are likely to find bling and coins. As long as you feel safe doing it I'd say to go for it.
As a side note, the book "The Urban Treasure Hunter" by Micahel Chapman is an interesting read that has some neat stories about city hunting. If you asked him he'd tell you to go for it!
Tried one over by Metro Center behind a buddys house. Took almost 30 minutes to get 4" for a clad almost like trying to dig through calieche with a teaspoon. After that I've seen Qwest & Cox crews in the alleys, They always have a jackhammer. I figure 20 - 30 years of heavy city trash trucks and the junk collectors packs it pretty good. Might not be that compacted in other areas though.