Eu tinha um código funcionando que usava as Atualizações de reconhecimento de atividade do Google. Agora, de repente, eles parecem enviar atualizações várias vezes por segundo ou nunca, embora solicitadas a cada 20 segundos. Não alterei o código e verifiquei as versões anteriores, mas tenho o mesmo problema.

Criei um exemplo mínimo a partir do tutorial, mas também não recebo atualizações de atividades com meu dispositivo Nexus 5. Com o meu HTC Desire (MildWild 5.0 baseado no Android 2.3.7), ele funciona perfeitamente bem. Suspeitei do Google Play Services, mas ambos os telefones têm a versão 4.2.43 instalada

Atividade principal:

package com.example.testactivities;
import android.app.PendingIntent;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.util.Log;
import android.view.Menu;

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesClient.ConnectionCallbacks;
import com.google.android.gms.common.GooglePlayServicesClient.OnConnectionFailedListener;
import com.google.android.gms.location.ActivityRecognitionClient;

public class MainActivity extends FragmentActivity implements
ConnectionCallbacks, OnConnectionFailedListener {
    // Constants that define the activity detection interval
    public static final int MILLISECONDS_PER_SECOND = 1000;
    public static final int DETECTION_INTERVAL_SECONDS = 1;
    public static final int DETECTION_INTERVAL_MILLISECONDS = 
            MILLISECONDS_PER_SECOND * DETECTION_INTERVAL_SECONDS;
    /*
     * Store the PendingIntent used to send activity recognition events
     * back to the app
     */
    private PendingIntent mActivityRecognitionPendingIntent;
    // Store the current activity recognition client
    private ActivityRecognitionClient mActivityRecognitionClient;
    // Flag that indicates if a request is underway.
    private boolean mInProgress;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        /*
         * Instantiate a new activity recognition client. Since the
         * parent Activity implements the connection listener and
         * connection failure listener, the constructor uses "this"
         * to specify the values of those parameters.
         */
        mActivityRecognitionClient =
                new ActivityRecognitionClient(this, this, this);
        /*
         * Create the PendingIntent that Location Services uses
         * to send activity recognition updates back to this app.
         */
        Intent intent = new Intent(
                this.getApplicationContext(), ActivityRecognitionIntentService.class);
        /*
         * Return a PendingIntent that starts the IntentService.
         */
        mActivityRecognitionPendingIntent =
                PendingIntent.getService(this, 0, intent,
                PendingIntent.FLAG_UPDATE_CURRENT);
        // Start with the request flag set to false
        mInProgress = false;
        this.startUpdates();
    }

    /**
     * Request activity recognition updates based on the current
     * detection interval.
     *
     */
     public void startUpdates() {
        // If a request is not already underway
        if (!mInProgress) {
            // Indicate that a request is in progress
            mInProgress = true;
            // Request a connection to Location Services
            mActivityRecognitionClient.connect();
        //
        } else {
            /*
             * A request is already underway. You can handle
             * this situation by disconnecting the client,
             * re-setting the flag, and then re-trying the
             * request.
             */
        }
    }

     /*
      * Called by Location Services once the location client is connected.
      *
      * Continue by requesting activity updates.
      */
     @Override
     public void onConnected(Bundle dataBundle) {
         Log.v("EXAMPLE","connected");
         /*
          * Request activity recognition updates using the preset
          * detection interval and PendingIntent. This call is
          * synchronous.
          */
         mActivityRecognitionClient.requestActivityUpdates(
                 DETECTION_INTERVAL_MILLISECONDS,
                 mActivityRecognitionPendingIntent);
         /*
          * Since the preceding call is synchronous, turn off the
          * in progress flag and disconnect the client
          */
         mInProgress = false;
         mActivityRecognitionClient.disconnect();
     }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public void onConnectionFailed(ConnectionResult arg0) {
        Log.v("EXAMPLE","Connection failed");

    }

    @Override
    public void onDisconnected() {
        Log.v("EXAMPLE","Disconnected");
    }

}

Manifesto:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.testactivities"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="10"
        android:targetSdkVersion="19" />
    <uses-permission android:name="com.google.android.gms.permission.ACTIVITY_RECOGNITION"/>

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <meta-data
            android:name="com.google.android.gms.version"
            android:value="@integer/google_play_services_version" />
        <activity
            android:name="com.example.testactivities.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <service
            android:name="com.example.testactivities.ActivityRecognitionIntentService"/>
    </application>

</manifest>

RecognitionIntentService:

package com.example.testactivities;

import android.app.IntentService;
import android.content.Intent;
import android.util.Log;

public class ActivityRecognitionIntentService extends IntentService {

    public ActivityRecognitionIntentService() {
        super("ActivityRecognitionIntent");
        Log.v("EXAMPLE","constructor");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        Log.v("EXAMPLE","new activity update");
    }

}

ATUALIZAÇÃO: Acredito que o canopi identificou o problema correto. Quando o dispositivo ainda está com alta confiança, ele não dispara nenhuma intenção de reconhecimento. Definitivamente, isso foi diferente há um ano (em outros dispositivos). Para detectar se o dispositivo ainda está, registro a última atividade recebida com seu carimbo de data e hora e verifico periodicamente isso. Um registro de data e hora antigo indica que o dispositivo ainda está parado naquele tempo.