RxComboDetector.java

static Observable<Integer> detect(Observable<Void> clicks, final long maxIntervalMillis,
        final int minComboTimesCared) {
    return clicks.map(new Func1<Void, Integer>() {
            @Override
            public Integer call(Void aVoid) {
                return 1;
            }
        }).timestamp()
        .scan(new Func2<Timestamped<Integer>, Timestamped<Integer>, Timestamped<Integer>>() {
            @Override
            public Timestamped<Integer> call(Timestamped<Integer> lastOne,
                    Timestamped<Integer> thisOne) {
                if (thisOne.getTimestampMillis() - lastOne.getTimestampMillis() <=
                        maxIntervalMillis) {
                    return new Timestamped<>(thisOne.getTimestampMillis(),
                            lastOne.getValue() + 1);
                } else {
                    return new Timestamped<>(thisOne.getTimestampMillis(), 1);
                }
            }
        }).map(new Func1<Timestamped<Integer>, Integer>() {
            @Override
            public Integer call(Timestamped<Integer> timestamped) {
                return timestamped.getValue();
            }
        }).filter(new Func1<Integer, Boolean>() {
            @Override
            public Boolean call(Integer combo) {
                return combo >= minComboTimesCared;
            }
        });
}

RxComboDetectorDemo.java

new RxComboDetector.Builder()
    .maxIntervalMillis(500)
    .minComboTimesCared(3)
    .detectOn(mBtnCombo)
    .start()
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe(new Action1<Integer>() {
        @Override
        public void call(Integer combo) {
            // do something
        }
    });