diff --git a/app/views/stopwatch/_settings.html.erb b/app/views/stopwatch/_settings.html.erb
new file mode 100644
index 0000000..873d442
--- /dev/null
+++ b/app/views/stopwatch/_settings.html.erb
@@ -0,0 +1,4 @@
+<p>
+  <label for="settings_default_activity"><%= t '.label_default_activity' %> </label>
+  <%= select_tag 'settings[default_activity]', options_from_collection_for_select( [['always_ask', t('.label_always_ask')], ['system', t('.label_system')]] + TimeEntryActivity.system.active.to_a.pluck(:id, :name), :first, :last, Stopwatch.settings['default_activity'] ) %>
+</p>
diff --git a/init.rb b/init.rb
index 7b68dd0..c634f6e 100644
--- a/init.rb
+++ b/init.rb
@@ -1,3 +1,4 @@
+require_dependency 'stopwatch'
 require 'stopwatch/hooks'
 
 Redmine::Plugin.register :stopwatch do
@@ -8,6 +9,9 @@ Redmine::Plugin.register :stopwatch do
   version '0.1.0'
 
   requires_redmine version_or_higher: '3.4.0'
+  settings default: {
+    'default_activity' => 'always_ask',
+  }, partial: 'stopwatch/settings'
 
   menu :account_menu, :stopwatch,
     :new_stopwatch_timer_path,
diff --git a/lib/stopwatch.rb b/lib/stopwatch.rb
index 0b14ec8..723e8f5 100644
--- a/lib/stopwatch.rb
+++ b/lib/stopwatch.rb
@@ -1,2 +1,36 @@
+# frozen_string_literal: true
+
 module Stopwatch
+  def self.settings
+    Setting.plugin_stopwatch
+  end
+
+  def self.default_activity
+    if id = settings['default_activity'].presence
+      if id.to_s =~ /^\d+$/
+        TimeEntryActivity.find_by_id id
+      else
+        id
+      end
+    end
+  end
+
+  def self.default_activity_for(time_entry)
+    default = Stopwatch.default_activity
+    return nil if default == 'always_ask'
+
+    project = time_entry.project || time_entry.issue&.project
+
+    if project.nil?
+      activities = TimeEntryActivity.shared.active
+    else
+      activities = project.activities
+    end
+
+    if default == 'system'
+      activities.detect(&:is_default?) || activities.detect{|a| a.parent&.is_default?} || (activities.one? && activities[0]).presence
+    else
+      return activities.detect{ |a| a == default || a.parent == default }
+    end
+  end
 end
diff --git a/test/unit/stopwatch_test.rb b/test/unit/stopwatch_test.rb
new file mode 100644
index 0000000..78944c3
--- /dev/null
+++ b/test/unit/stopwatch_test.rb
@@ -0,0 +1,78 @@
+require_relative '../test_helper'
+
+class StopwatchTest < ActiveSupport::TestCase
+  fixtures :projects, :enabled_modules, :enumerations
+
+  setup do
+    @project = Project.find 'ecookbook'
+    @te = TimeEntry.new project: @project
+  end
+
+  test "default value for default_activity" do
+    assert_equal 'always_ask', Stopwatch.default_activity
+  end
+
+  test "should find default activity" do
+    with_settings plugin_stopwatch: { 'default_activity' => 9} do
+      assert_equal 'Design', Stopwatch.default_activity.name
+    end
+    with_settings plugin_stopwatch: { 'default_activity' => '11'} do
+      assert_equal 'QA', Stopwatch.default_activity.name
+    end
+  end
+
+  ### 'system' -> ask if there is no sys default / more than one availabale activity
+
+  test "should use system default activity for te" do
+    with_settings plugin_stopwatch: { 'default_activity' => 'system' } do
+      assert_equal 'Development', Stopwatch.default_activity_for(@te).name
+    end
+  end
+
+  test "should use single active project activity for time entry" do
+    with_settings plugin_stopwatch: { 'default_activity' => 'system' } do
+      TimeEntryActivity.create! active: false, project: @project, name: 'Development', parent_id: 10
+      TimeEntryActivity.create! active: false, project: @project, name: 'QA', parent_id: 11
+      assert_equal 'Design', Stopwatch.default_activity_for(@te).name
+    end
+  end
+
+  test "should ask if more than one and no default" do
+    with_settings plugin_stopwatch: { 'default_activity' => 'system' } do
+      TimeEntryActivity.update_all is_default: false
+      assert_nil Stopwatch.default_activity_for(@te)
+    end
+  end
+
+  ### always_ask (the default)
+
+  test "should return nil if always ask is set" do
+    assert_nil Stopwatch.default_activity_for(@te)
+
+    TimeEntryActivity.create! active: false, project: @project, name: 'Development'
+    assert_nil Stopwatch.default_activity_for(@te)
+
+    TimeEntryActivity.where(name: 'Development').delete_all
+    assert_nil Stopwatch.default_activity_for(@te)
+  end
+
+  ### specific activity -> ask only if this is not available in project
+
+  test "should use configured default activity for time entry" do
+    with_settings plugin_stopwatch: { 'default_activity' => '9' } do
+      assert_equal 'Design', Stopwatch.default_activity_for(@te).name
+    end
+  end
+
+  test "should not have default if unavailable" do
+    TimeEntryActivity.create! active: false, project: @project, name: 'Design', parent_id: 9
+    TimeEntryActivity.create! active: false, project: @project, name: 'Development', parent_id: 11
+    assert_equal [10], @project.activities.pluck(:id)
+
+    with_settings plugin_stopwatch: { 'default_activity' => '9'} do
+      assert_nil Stopwatch.default_activity_for(@te)
+    end
+  end
+
+end
+