RxAccountBus.java

public class RxAccountBus {
    private final static RxAccountBus INSTANCE = new RxAccountBus();

    public final static int ACCOUNT_LOGGED_IN = 0;
    public final static int ACCOUNT_LOGGED_OUT = 1;
    public final static int ACCOUNT_DATA_UPDATED = 2;

    @Retention(SOURCE)
    @IntDef({ACCOUNT_LOGGED_IN, ACCOUNT_LOGGED_OUT, ACCOUNT_DATA_UPDATED})
    public @interface Account {
    }

    private PublishSubject<Integer> subject = PublishSubject.create();

    private RxAccountBus() {
        // nothing to do here
    }

    public static RxAccountBus getInstance() {
        return INSTANCE;
    }

    /**
     * Pass any event down to event listeners.
     */
    public void sendEvent(@Account int account) {
        subject.onNext(account);
    }

    /**
     * Subscribe to this Observable.
     */
    public Observable<Integer> getEvents() {
        return subject;
    }
}

you might want to use return subject.asObservable(); instead than just return subject;