Is the security deposit refundable if you don't move in?

It depends on what the lease says. If the deposit was intended to reimburse the landlord for damages caused to the premises, then you might be entitled to get it back. It is more likely that the deposit was to secure amounts due under the lease. If you signed it and didn't move in, and it is still not rented, then the landlord is entitled to keep it, I think.

I agree with the previous response in that it depends on your lease language. A Landlord can request a security deposit to hold a a rental for a tenant at the time the tenant fills in the rental application. Read your application/lease carefully concerning the refundability of the deposit as that is what will control. Generally, if the tenant changes their mind about leasing the premises, (even before the lease is signed) the deposit may not, in certain instances, be returned if the Landlord has not found a replacement tenant before your move-in date. It's likely under these facts your Landlord would be allowed to keep the deposit as he lost rental income when you backed out of the lease. He is actually required under the law to begin showing the premises again to mitigate his damages. Technically, if you signed the lease and then backed out not only can he charge to the security deposit to your unpaid rent, but he can often hold you to the rental obligations under the contract each month until it can be rented by someone else.