NSString *filePath = @"/Applications/Cydia.app";
if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]){
    Lable.text = @"You are jailbroken";
    Button.enabled = YES;
}

if ([[UIApplication sharedApplication] canOpenURL:[NSURL URLWithString:@"cydia://"]]){
     Lable.text = @"You are jailbroken";
     Button.enabled = YES;
}

NSString* filePath = [NSSearchPathForDirectoriesInDomains(NSApplicationDirectory, NSUserDomainMask, YES) stringByAppendingPathComponent: @"cydia.app"];