diff --git a/app/controllers/users/profiles_controller.rb b/app/controllers/users/profiles_controller.rb
index 96015d55..9f3726a7 100644
--- a/app/controllers/users/profiles_controller.rb
+++ b/app/controllers/users/profiles_controller.rb
@@ -8,6 +8,8 @@ class Users::ProfilesController < ApplicationController
 
   def update
     @user.update user_params
+    disconnect_remote_connections if @user.saved_change_to_password_digest?
+
     redirect_to user_profile_url, notice: update_notice
   end
 
diff --git a/app/models/user.rb b/app/models/user.rb
index df2fee19..449ab02b 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -20,6 +20,7 @@ class User < ApplicationRecord
   has_secure_password validations: false
 
   after_create_commit :grant_membership_to_open_rooms
+  after_update :sign_out_other_sessions, if: :saved_change_to_password_digest?
 
   scope :ordered, -> { order("LOWER(name)") }
   scope :filtered_by, ->(query) { where("name like ?", "%#{query}%") }
@@ -50,6 +51,12 @@ class User < ApplicationRecord
   end
 
   private
+    # A new password is how someone shuts out whoever else got into their account, so it ends the sessions opened
+    # with the old one. The session it was changed from, if any, stays.
+    def sign_out_other_sessions
+      sessions.excluding(Current.session).delete_all
+    end
+
     # One statement, which SQLite runs under the write lock, so no room is closed between reading the open ones and
     # inserting. A room that Room#destroy_later closes is either closed before, and skipped, or after, and takes this
     # membership away with the others. A room that granted itself to every user when it was created is skipped too,
diff --git a/test/controllers/cached_responses_test.rb b/test/controllers/cached_responses_test.rb
index 888994d0..df4102c4 100644
--- a/test/controllers/cached_responses_test.rb
+++ b/test/controllers/cached_responses_test.rb
@@ -136,6 +136,29 @@ class CachedResponsesTest < ActionDispatch::IntegrationTest
     assert_redirected_to new_session_url
   end
 
+  test "a session signed out by a password change isn't served from a cached snapshot or page" do
+    other_device = open_session { |session| session.host! "once.campfire.test" }
+    other_device.post session_url, params: { email_address: users(:david).email_address, password: "secret123456" }
+    other_device.get user_sidebar_url(:me)
+    other_device.assert_response :success
+
+    Session.expects(:find_by).never
+    ResponseCache.instance.expects(:write).never
+    other_device.get user_sidebar_url(:me)
+    other_device.assert_response :success
+    Session.unstub(:find_by)
+    ResponseCache.instance.unstub(:write)
+
+    put user_profile_url, params: { user: { password: "a new secret123456" } },
+      headers: { "Sec-Fetch-Site" => "same-origin", "Origin" => "http://once.campfire.test" }
+    assert_redirected_to user_profile_url
+
+    other_device.get user_sidebar_url(:me)
+    other_device.assert_redirected_to new_session_url
+    get user_sidebar_url(:me)
+    assert_response :success
+  end
+
   test "conditional requests keep native validators" do
     get room_messages_url(@room)
     etag = response.headers["ETag"]
diff --git a/test/controllers/users/profiles_controller_test.rb b/test/controllers/users/profiles_controller_test.rb
index 0331aafb..c5f95614 100644
--- a/test/controllers/users/profiles_controller_test.rb
+++ b/test/controllers/users/profiles_controller_test.rb
@@ -27,6 +27,52 @@ class Users::ProfilesControllerTest < ActionDispatch::IntegrationTest
     assert_equal "david@37signals.com", users(:david).email_address
   end
 
+  test "changing the password signs out the account's other sessions but not this one" do
+    other_device = open_session
+    other_device.post session_url, params: { email_address: users(:david).email_address, password: "secret123456" }
+    other_device.get user_profile_url
+    other_device.assert_response :success
+
+    put user_profile_url, params: { user: { password: "a new secret123456" } }
+    assert_redirected_to user_profile_url
+
+    other_device.get user_profile_url
+    other_device.assert_redirected_to new_session_url
+    get user_profile_url
+    assert_response :success
+    assert_equal 1, users(:david).sessions.count
+  end
+
+  test "changing the password closes the account's live connections" do
+    remote_connections = mock
+    remote_connections.expects(:disconnect).with(reconnect: true)
+    ActionCable.server.stubs(:remote_connections).returns(mock.tap { |m| m.expects(:where).with(current_user: users(:david)).returns(remote_connections) })
+
+    put user_profile_url, params: { user: { password: "a new secret123456" } }
+
+    assert_redirected_to user_profile_url
+  end
+
+  test "changing the password still signs out other sessions when the realtime service is unreachable" do
+    other_session = users(:david).sessions.first
+    ActionCable.server.stubs(:remote_connections).raises(RuntimeError.new("cable down"))
+
+    put user_profile_url, params: { user: { password: "a new secret123456" } }
+
+    assert_redirected_to user_profile_url
+    assert_not Session.exists?(other_session.id)
+  end
+
+  test "updating the profile without a new password leaves other sessions signed in" do
+    ActionCable.server.expects(:remote_connections).never
+
+    assert_no_difference -> { users(:david).sessions.count } do
+      put user_profile_url, params: { user: { name: "David", password: "" } }
+    end
+
+    assert_redirected_to user_profile_url
+  end
+
   test "updates are limited to the current user" do
     put user_profile_url(users(:jason)), params: { user: { name: "John Doe" } }
 
diff --git a/test/models/user_test.rb b/test/models/user_test.rb
index 61bb1c39..0926adaa 100644
--- a/test/models/user_test.rb
+++ b/test/models/user_test.rb
@@ -42,6 +42,28 @@ class UserTest < ActiveSupport::TestCase
     end
   end
 
+  test "changing the password outside a request signs out every session" do
+    users(:david).sessions.start!(user_agent: "Other device", ip_address: "127.0.0.1")
+
+    assert_changes -> { users(:david).sessions.count }, to: 0 do
+      users(:david).update!(password: "a new secret123456")
+    end
+  end
+
+  test "changing the password keeps the session it was changed from" do
+    Current.session = users(:david).sessions.start!(user_agent: "This device", ip_address: "127.0.0.1")
+
+    users(:david).update!(password: "a new secret123456")
+
+    assert_equal [ Current.session ], users(:david).sessions.reload
+  end
+
+  test "changing other details keeps every session" do
+    assert_no_changes -> { users(:david).sessions.count } do
+      users(:david).update!(name: "Dave", email_address: "dave@37signals.com")
+    end
+  end
+
   private
     def create_new_user
       User.create!(name: "User", email_address: "user@example.com", password: "secret123456")