diff --git a/changelog.d/1941.added.md b/changelog.d/1941.added.md
index 72e583006..7fea5d07d 100644
--- a/changelog.d/1941.added.md
+++ b/changelog.d/1941.added.md
@@ -1,2 +1,3 @@
-Added a way to to store expected heartbeat frequency (in seconds, minimum 60)
-to a source system, and made the new field visible in the admin.
+Added a way to to store expected heartbeat frequency (as a Postgres interval,
+minimum 60 seconds) to a source system, and made the new field visible in the
+admin.
diff --git a/changelog.d/1962.added.md b/changelog.d/1962.added.md
new file mode 100644
index 000000000..26148c944
--- /dev/null
+++ b/changelog.d/1962.added.md
@@ -0,0 +1 @@
+Show `last_seen` and `heartbeat_frequency` in the source list and allow altering `heartbeat_frequency`.
diff --git a/src/argus/htmx/sourcesystem/forms.py b/src/argus/htmx/sourcesystem/forms.py
index 68c61f776..e9e45db33 100644
--- a/src/argus/htmx/sourcesystem/forms.py
+++ b/src/argus/htmx/sourcesystem/forms.py
@@ -9,16 +9,18 @@ class Meta(AddSourceSystemForm.Meta):
         widgets = {
             "name": forms.TextInput,
             "base_url": forms.TextInput,
+            "heartbeat_frequency": forms.TextInput(attrs={"placeholder": "00:01:00"}),
         }
 
 
 class UpdateSourceSystemForm(forms.ModelForm):
     class Meta:
         model = SourceSystem
-        fields = ["name", "type", "base_url"]
+        fields = ["name", "type", "base_url", "heartbeat_frequency"]
         widgets = {
             "name": forms.TextInput,
             "base_url": forms.TextInput,
+            "heartbeat_frequency": forms.TextInput(attrs={"placeholder": "00:01:00"}),
         }
 
 
diff --git a/src/argus/htmx/templates/htmx/sourcesystem/_sourcesystem_row.html b/src/argus/htmx/templates/htmx/sourcesystem/_sourcesystem_row.html
index 1517a40ee..be0379f91 100644
--- a/src/argus/htmx/templates/htmx/sourcesystem/_sourcesystem_row.html
+++ b/src/argus/htmx/templates/htmx/sourcesystem/_sourcesystem_row.html
@@ -1,3 +1,4 @@
+{% load argus_htmx %}
 <tbody id="source-{{ source.pk }}"
        class="[&:last-child_tr:last-child_td]:border-b-0">
   <tr>
@@ -8,6 +9,12 @@
     <td class="{% if not generated_token %}border-b border-base-300{% endif %} max-w-xs truncate">
       {{ source.base_url|default:"-" }}
     </td>
+    <td class="{% if not generated_token %}border-b border-base-300{% endif %} max-w-xs truncate">
+      {{ source.last_seen|default:"Never" }}
+    </td>
+    <td class="{% if not generated_token %}border-b border-base-300{% endif %} max-w-xs truncate">
+      {{ source.heartbeat_frequency|pretty_timedelta:"Off" }}
+    </td>
     <td class="{% if not generated_token %}border-b border-base-300{% endif %}">
       {% if source.token_status == "valid" %}
         <span class="badge badge-outline badge-success text-xs gap-1">
diff --git a/src/argus/htmx/templates/htmx/sourcesystem/sourcesystem_form.html b/src/argus/htmx/templates/htmx/sourcesystem/sourcesystem_form.html
index 7cee4bf0c..27d101e25 100644
--- a/src/argus/htmx/templates/htmx/sourcesystem/sourcesystem_form.html
+++ b/src/argus/htmx/templates/htmx/sourcesystem/sourcesystem_form.html
@@ -78,6 +78,66 @@ <h2 class="card-title">
                 </div>
               {% endif %}
             </div>
+            <div class="form-control w-full">
+              <label class="label" for="{{ form.heartbeat_frequency.auto_id }}">
+                <span class="label-text"><em>Heartbeat frequency</em></span>
+              </label>
+              {% render_field form.heartbeat_frequency class+="input input-bordered w-full" %}
+              {% if form.heartbeat_frequency.help_text %}
+                <div class="label">
+                  <div class="label-text-alt">
+                    <p>Expected to send heartbeat at least every N seconds. Lower bound: 60 seconds. Upper bound: 1 day.</p>
+                    <table class="table table-sm">
+                      <thead>
+                        <tr>
+                          <th scope="col">Valid inputs</th>
+                          <th scope="col">Short</th>
+                          <th scope="col">Long</th>
+                          <th scope="col">Notes</th>
+                        </tr>
+                      </thead>
+                      <tbody>
+                        <tr>
+                          <th scope="row">seconds as an integer</th>
+                          <td>1000</td>
+                          <td>86400</td>
+                          <td></td>
+                        </tr>
+                        <tr>
+                          <th scope="row">DD HH:MM:SS</th>
+                          <td>00:16:40</td>
+                          <td>1 00:00:00</td>
+                          <td>This is the format that is displayed in the form</td>
+                        </tr>
+                        <tr>
+                          <th scope="row">
+                            <a href="https://en.wikipedia.org/wiki/ISO_8601#Durations">ISO 8601 periods</a>
+                          </th>
+                          <td>PT16M40S</td>
+                          <td>P1D</td>
+                          <td>The T is needed if less than a day.</td>
+                        </tr>
+                        <tr>
+                          <th scope="row">
+                            <a href="https://www.postgresql.org/docs/current/datatype-datetime.html#DATATYPE-INTERVAL-INPUT">PostgreSQL’s day-time interval format</a>
+                          </th>
+                          <td>00:16:40</td>
+                          <td>1 day 00:00:00</td>
+                          <td></td>
+                        </tr>
+                      </tbody>
+                    </table>
+                  </div>
+                </div>
+              {% endif %}
+              {% if form.heartbeat_frequency.errors %}
+                <div class="label">
+                  {% for error in form.heartbeat_frequency.errors %}
+                    <span class="label-text-alt text-error">{{ error }}</span>
+                  {% endfor %}
+                </div>
+              {% endif %}
+            </div>
           </div>
           <div class="card-actions justify-end mt-6">
             <button type="submit" class="btn btn-primary">
diff --git a/src/argus/htmx/templates/htmx/sourcesystem/sourcesystem_list.html b/src/argus/htmx/templates/htmx/sourcesystem/sourcesystem_list.html
index 9e973481d..c71ca7907 100644
--- a/src/argus/htmx/templates/htmx/sourcesystem/sourcesystem_list.html
+++ b/src/argus/htmx/templates/htmx/sourcesystem/sourcesystem_list.html
@@ -13,6 +13,8 @@
           <th class="border-b border-primary">Name</th>
           <th class="border-b border-primary">Type</th>
           <th class="border-b border-primary">Base URL</th>
+          <th class="border-b border-primary">Last seen</th>
+          <th class="border-b border-primary">Heartbeat</th>
           <th class="border-b border-primary">Token</th>
           <th class="border-b border-primary text-right">Incidents</th>
           <th class="border-b border-primary text-right">Actions</th>
diff --git a/src/argus/htmx/templatetags/argus_htmx.py b/src/argus/htmx/templatetags/argus_htmx.py
index b9750534e..5c9803751 100644
--- a/src/argus/htmx/templatetags/argus_htmx.py
+++ b/src/argus/htmx/templatetags/argus_htmx.py
@@ -1,9 +1,13 @@
+from datetime import timedelta
 from typing import Literal
+
 from django import template
 from django.contrib.messages.storage.base import Message
 from django.conf import settings
 from django.core.exceptions import ValidationError
 from django.core.validators import URLValidator
+from django.utils.timesince import timesince, timeuntil
+from django.utils.timezone import now as tznow
 
 from .. import defaults
 
@@ -99,3 +103,18 @@ def is_valid_url(value: str) -> bool:
         return True
     except ValidationError:
         return False
+
+
+@register.filter
+def pretty_timedelta(value: timedelta, fallback: str = "") -> str:
+    '''Humanize a timedelta with the same alogrithm as "timesince"'''
+
+    if value is None:
+        return fallback
+    now = tznow()
+    then = now + value
+    if now > then:
+        return timesince(now, then)
+    if now < then:
+        return timeuntil(then, now)
+    return "0\xa0minutes"
diff --git a/src/argus/incident/migrations/0003_sourcesystem_heartbeat_frequency.py b/src/argus/incident/migrations/0003_sourcesystem_heartbeat_frequency.py
index a0d5fe105..1648159f7 100644
--- a/src/argus/incident/migrations/0003_sourcesystem_heartbeat_frequency.py
+++ b/src/argus/incident/migrations/0003_sourcesystem_heartbeat_frequency.py
@@ -1,5 +1,6 @@
-# Generated by Django 5.2.13 on 2026-06-15 11:46
+# Generated by Django 5.2.13 on 2026-06-22 12:05
 
+import datetime
 import django.core.validators
 from django.db import migrations, models
 
@@ -14,6 +15,6 @@ class Migration(migrations.Migration):
         migrations.AddField(
             model_name='sourcesystem',
             name='heartbeat_frequency',
-            field=models.IntegerField(blank=True, help_text='Expected to send heartbeat at least every N seconds, lower bound: 60 seconds', null=True, validators=[django.core.validators.MinValueValidator(60)]),
+            field=models.DurationField(blank=True, help_text="Expected to send heartbeat at least every N seconds. Lower bound: 60 seconds. Upper bound: 1 day. Valid inputs: seconds (as an integer, e.g. 86400), DD HH:MM:SS (1 00:00:00), ISO 8601 periods (P1D, note the T is needed if less than a day), PostgreSQL's day-time interval format (1 day)", null=True, validators=[django.core.validators.MinValueValidator(datetime.timedelta(seconds=60)), django.core.validators.MaxValueValidator(datetime.timedelta(days=1))]),
         ),
     ]
diff --git a/src/argus/incident/models.py b/src/argus/incident/models.py
index 5adf27385..0e134f909 100644
--- a/src/argus/incident/models.py
+++ b/src/argus/incident/models.py
@@ -9,7 +9,7 @@
 
 from django.contrib.auth import get_user_model
 from django.core.exceptions import ValidationError
-from django.core.validators import URLValidator, MinValueValidator
+from django.core.validators import MaxValueValidator, MinValueValidator, URLValidator
 from django.db import models
 from django.db.models import F, Q
 from django.utils import timezone
@@ -18,9 +18,11 @@
 from argus.util.datetime_utils import INFINITY_REPR, get_infinity_repr
 from .constants import Level
 from .fields import DateTimeInfinityField
-from .validators import validate_lowercase, validate_key
+from .validators import validate_key, validate_lowercase
 
 
+MINIMUM_DURATION = timedelta(seconds=60)
+MAXIMUM_DURATION = timedelta(days=1)
 LOG = logging.getLogger(__name__)
 User = get_user_model()
 
@@ -165,11 +167,14 @@ class SourceSystem(models.Model):
         blank=True,
     )
     last_seen = models.DateTimeField(null=True, blank=True)
-    heartbeat_frequency = models.IntegerField(
+    heartbeat_frequency = models.DurationField(
         blank=True,
         null=True,
-        help_text="Expected to send heartbeat at least every N seconds, lower bound: 60 seconds",
-        validators=[MinValueValidator(60)],
+        help_text="Expected to send heartbeat at least every N seconds. Lower bound: 60 seconds. Upper bound: 1 day. Valid inputs: seconds (as an integer, e.g. 86400), DD HH:MM:SS (1 00:00:00), ISO 8601 periods (P1D, note the T is needed if less than a day), PostgreSQL's day-time interval format (1 day)",
+        validators=[
+            MinValueValidator(MINIMUM_DURATION),
+            MaxValueValidator(MAXIMUM_DURATION),
+        ],
     )
 
     class Meta:
diff --git a/tests/htmx/test_templatetags.py b/tests/htmx/test_templatetags.py
index 4ae42fab7..07c23cef4 100644
--- a/tests/htmx/test_templatetags.py
+++ b/tests/htmx/test_templatetags.py
@@ -1,8 +1,9 @@
 from unittest import TestCase
+from datetime import timedelta
 
 from django.test import tag
 
-from argus.htmx.templatetags.argus_htmx import dictvalue
+from argus.htmx.templatetags.argus_htmx import dictvalue, pretty_timedelta
 
 
 @tag("unit")
@@ -18,3 +19,30 @@ def test_get_value_from_dict_when_key_is_missing_returns_None(self):
     def test_get_value_from_dict_when_key_is_missing_and_default_is_set_returns_default(self):
         testdict = {}
         self.assertEqual(dictvalue(testdict, 1, "boo"), "boo")
+
+
+@tag("unit")
+class PrettyTimedeltaTest(TestCase):
+    def test_pretty_timedelta_when_value_is_None_return_fallback(self):
+        result = pretty_timedelta(None, "foo")
+        self.assertEqual(result, "foo")
+
+    def test_when_value_is_zero_return_constant_string(self):
+        result = pretty_timedelta(timedelta(seconds=0))
+        self.assertEqual(result, "0\xa0minutes")
+
+    def test_when_value_is_positive_return_calculated_string(self):
+        result = pretty_timedelta(timedelta(seconds=1))
+        self.assertEqual(result, "0\xa0minutes")
+        result = pretty_timedelta(timedelta(seconds=10))
+        self.assertEqual(result, "0\xa0minutes")
+        result = pretty_timedelta(timedelta(seconds=100000))
+        self.assertEqual(result, "1\xa0day, 3\xa0hours")
+
+    def test_when_value_is_negative_return_0_minutes(self):
+        result = pretty_timedelta(timedelta(seconds=-1))
+        self.assertEqual(result, "0\xa0minutes")
+        result = pretty_timedelta(timedelta(seconds=-10))
+        self.assertEqual(result, "0\xa0minutes")
+        result = pretty_timedelta(timedelta(seconds=-100000))
+        self.assertEqual(result, "0\xa0minutes")