diff --git a/lib/RevBank/Plugins.pod b/lib/RevBank/Plugins.pod
index 6daac5a..38ba189 100644
--- a/lib/RevBank/Plugins.pod
+++ b/lib/RevBank/Plugins.pod
@@ -189,6 +189,20 @@ Called when a new user account was created.
 
 Called when a user account is updated.
 
+=item hook_product_changed($class, $old, $new, $mtime, @)
+
+Called when a product is changed. For new products, C<$old> will be undef.
+
+Caveats: Only things that change during runtime cause this hook to be called. When multiple revbank instances are running, each process gets this hook. When the products file is modified externally, the new file is loaded only after user interaction. When a product's primary id changes, it is registerd as a deletion and addition, not a change.
+
+The mtime is the mtime of the products file, not necessarily when the product was changed.
+
+=item hook_product_deleted($class, $product, $mtime, @)
+
+Called when a product is deleted.
+
+The same caveats like for C<hook_product_changed> apply.
+
 =back
 
 Default messages can be silenced by overriding the hooks in
diff --git a/lib/RevBank/Products.pm b/lib/RevBank/Products.pm
index 9e29be9..29e0bff 100644
--- a/lib/RevBank/Products.pm
+++ b/lib/RevBank/Products.pm
@@ -9,19 +9,20 @@ use RevBank::Global;
 use Exporter qw(import);
 our @EXPORT = qw(read_products);
 
+# Note: the parameters are subject to change
 sub read_products($filename = "revbank.products", $default_contra = "+sales/products") {
-    state %cache;   # $filename => \%products
+    state %caches;   # $filename => \%products
     state %mtimes;  # $filename => mtime
 
     my $mtime = \$mtimes{$filename};
-
-    return $cache{$filename} if $$mtime and $$mtime == -M $filename;
+    my $cache = $caches{$filename} ||= {};
+    return $cache if $$mtime and (stat $filename)[9] == $$mtime;
 
     my %products;
     my $linenr = 0;
     my $warnings = 0;
 
-    $$mtime = -M $filename;
+    $$mtime = (stat $filename)[9];
     for my $line (slurp $filename) {
         $linenr++;
 
@@ -102,6 +103,8 @@ sub read_products($filename = "revbank.products", $default_contra = "+sales/prod
             # HERE (see .pod)
             $products{$id} = {
                 id          => $ids[0],
+                aliases     => [ @ids[1 .. $#ids] ],
+                is_alias    => $id ne $ids[0],
                 description => $desc,
                 contra      => $contra || $default_contra,
                 _addon_ids  => \@addon_ids,
@@ -179,7 +182,27 @@ sub read_products($filename = "revbank.products", $default_contra = "+sales/prod
         $product->{total_price} = $tag_price + $hidden;
     }
 
-    return $cache{$filename} = \%products;
+    if (%$cache) {
+        for my $new (values %products) {
+            next if $new->{is_alias};
+
+            my $id = $new->{id};
+            my $old = $cache->{$id};
+
+            call_hooks("product_changed", $old, $new, $$mtime)
+                if not defined $old or $new->{config} ne $old->{config};
+
+            delete $cache->{$id};
+        }
+
+        for my $p (values %$cache) {
+            next if $p->{is_alias};
+            call_hooks("product_deleted", $p, $$mtime);
+        }
+    }
+
+    %$cache = %products;
+    return \%products;
 }
 
 1;